Irish Surnames

Gaelic Name - Anglicized name - Early County Origin - Other Roots

https://surnames.behindthename.com/names/usage/irish

Mac an Bhreitheamhan - (Mac) Abraham, Abrehan, Judge - Co Cork

Ó hEachthianna - Ahern or Hearne - Co Clare - the Dal gCais (e.g. Brian Boru)

Mac an tSaoir - MacAteer - Ulster, (St. Ciaran)

Mac Amhalghaidh - MacAuley or MacAwley - Co Offaly/Westmeath, lords of Calry

Mac Amhlaoibh - MacAuley or MacAwley - Co Fermanagh - branch of MaGuire

Mac Amhlaoibh - MacAuliffe - Co Cork - branch of MacCarthy

Mac Árdghail - MacArdle - County Monaghan, Armagh and Louth of Oriell

Ó Banain - O'Banan or O'Bannion - Co Fermanagh

Ó Banain - (O) Bannon or O'Bannion - Co Tipperary

Ó Beaglaoich - Begley - Co Donegal

Ó Birn - (O) Beirne - Co Roscommon - chiefs of Tir Briuin

Ó hAimheirgin - (O) Bergin - Co Offaly - chiefs of Geashill

Ó Beolláin - (O) Boland - Co Sligo - Uí Fiachrach

Ó Beolláin - (O) Boland - Co Clare - Dalcassian

Ó Baoghill - (O) Boyle - Co Donegal

Ó Baoighealláin - (O) Boylan - Fermanagh/Monaghan - same stock as O'Flanagans

Mac Bradaigh - Brady - Co Cavan

Ó Brollacháin - (O) Brallaghan or Bradley - Co Tyrone/Derry - Cinel Feradaigh

Mac Braoin - (Mac) Breen - Ossory, Co Kilkenny

Ó Braoin - (O) Breen - Westmeath/Offaly - Lord of Brawney

Mac an Bhreitheamhnaigh - (Mac) Breheny, Judge - Co Sligo/n. Roscommon

Mac Branain - MacBrennan - Co Roscommon - chiefs of Corca Achlann

Ó Braonain - (O) Brennan - Co Kilkenny, East Galway, Westmeath and Kerry

Ó Breislein - (O) Breslin - Co Donegal, Cenel Enda, chiefs of Fanad

Ó Bric - (O) Brick - Co Waterford - of the Decies

Ó Bruic - (O) Brick - Co Kerry - originally of Thomond

Mac Giolla Bhride - MacBride or Kilbride - Co Donegal

Ó Briain - O'Brien - Munster (Thomond) - the Uí Toirdealbhaigh, part of the Dal gCais

Ó Bruadiar - (O) Broder or Broderick - Co Cork, Limerick and Galway

Ó Brógáin - (O) Brogan - Co Mayo - the Uí Fiachrach

Ó Brolaigh - (O) Brolly, Brally, Brawley - Co Donegal/Derry - Cinel Oenghusa

Ó Bróithe - (O) Brophy - Co Kilkenny, Laois

Ó Brosnacháin - (O) Brosnan - Co Kerry

Ó Buachalla - Buckley - Co Tipperary/Offaly

Ó Bogaigh - Buggy - Co Kilkenny/Wexford (origin unknown)

Mac Conboirne - Burns - N. Connaught - mainly of Scottish origin

Ó Broin - (O) Byrne, Burns - Co Kildare/Wicklow - Uí Broin sept of Crioch Branach

Mac Cába - MacCabe or McCabe - Co Cavan, etc. - a Breffny sept from the western isles of Scotland

Mac Gafraidh - (Mac) Caffrey - Co Tyrone/Fermanagh - branch of the Maguires

Ó Cathain - O'Cahan or Kane - East Donegal - Cenel Eoghain

Ó Cathail - (O) Cahill - Co Galway - chief of Kinelea

Ó Cathail - (O) Cahill - Co Kerry and also in Tipperary

Ó Ceallacháin - (O) Callaghan - Co Cork - the Eoghanacht, descent from Ceallachan

Ó Cathaláin - (O) Callan - Co Monaghan/Louth - named from a king of Fernmag.

Mac Giolla Laoire - (Mac) Callery, Colleary, Collary - Co. Sligo & north Connacht

Mac Cathmhaoil - Campbell - Co Tyrone - Cenel Fearadhaigh Theas of Cenel Eoghain

Mac Cailein - Campbell - Co Donegal - Scottish gallowglass of Cenel Eoghain

Ó Ceanndubháin - (O) Canavan - Co Galway, physicians to O'Flaherty of Connemara

Mac Cuindlis - MacCandless - Co Down

Mac Anna or Canna- MacCann - Co Armagh - lords of Clanbrassil (Cenel Eoghain)

Ó Canain - (O) Cannon - Co Galway - the Uí Maine, same stock as O'Madden

Ó Canannain - (O) Cannon - Co Donegal - Kings of Cinel Conaill (pre-1200)

Ó Caithniadh - (O) Canny - Co Mayo - Uí Fiachrach Muaidhe, chiefs of Erris

Ó an Cháintigh - (O) Canty - west Co Cork

Ó Cairbre - (O) Carbery - Co Westmeath - chiefs in Clonlonan

Ó Ciardha - (O) Carey - Co Kildare - southern Uí Neill, lords of Carbury

Ó Cearmada - (O) Carmody - east Co Clare

Mac Cearnaigh - (Mac) Carney or Kearney - Co Meath and Monaghan/Armagh

Ó Cearrnaigh - (O) Carney - Co Mayo - Uí Fiachrach

Ó Cairealláin - (O) Carolan - Co Derry - chief of Clan Diarmada

Ó Cearbhalláin - (O) Carolan - Co Cavan/Monaghan

Ó Cairre - (O) Carr and (O) Carry - various, e.g. of Cenel Aengusa

Ó Cearbhaill - (O) Carroll - Co Offaly and Tipperary - lords of Eile (Ely)

Ó Cearbhaill - (O) Carroll - Co Monaghan and Louth - chiefs of Oriel

Ó Cearbhaill - (O) Carroll - Co Leitrim/Sligo - chief of Calraighe

Ó Cearbhaill - (O) Carroll - Co Kilkenny - chief of northern Gowran

Ó Cearbhaill - (O) Carroll - Co Kerry - chief of Locha Lein

Mac Cearbhaill - (Mac) Carroll or MacCarvill - Ulster

Mac Artian - MacCartan - Co Down - chiefs of Kinelarty

Mac Carthaigh - MacCarthy - Munster (Tipperary) - the Eoghanacht

* MacCarthy Mor - South Kerry

* Dunhallow MacCarthys - Northwest Cork

* MacCarthy Riabhach - Carberry, Southwest Cork

* MacCarthy Muskerry - Cork/Kerry border

Ó Cathasaigh - (O) Casey - various, including lords of Suaithni (co. Dublin)

Mac Cathasaigh - MacCasey or Casey - Co Louth/Monaghan

Ó Caiside - Cassidy - Co Fermanagh

Mac Fhlannchaidh - (Mac) Clancy - Co Clare - Dal gCais, branch of MacNamara

Mac Fhlannchaidh - (Mac) Clancy - Co Leitrim - chief of Dartry (Rosclogher)

Ó Cleireigh(Clery) - Clark(e) - Connacht, Donegal - chiefs of Uí Fiachra Finn

Ó Cléirigh - (O) Clery or Cleary - Co Galway - Tigherneach Ua Cleirigh, lord of Aidhne

Ó Cleirchín - (O) Clerkin, Clerk, Cleary - Co Limerick - Uí Fidhgeinte, Uí-Cairbre

Ó Clochasaigh - (O) Cloghessy, Clohessy - Clare Clare, east Limerick. Dalcassian

Mac Cluin - (Mac) Clune - Co Clare

Mac Bhloscaidh - McCluskey - Co Derry - a branch of the O'Cahans

Ó Cobhthaigh - (O) Coffey - Co Cork - same stock as O'Driscolls

Ó Cobhthaigh - (O) Coffey - Co Roscommon - Uí Maine branch of the O'Maddens

Ó Cobhthaigh - (O) Coffey - Co Westmeath

Mac Cagadhain - Cogan - Co Leitrim

Ó Colmáin - Coleman - Co Sligo, barony of Tireragh - Uí Fiachrach

Ó Clúmháin - Coleman or O'Colman - Co Sligo/Cork - descendant of Clumhan

Mac Colghain - (Kil) or (Mac) Colgan - Co Offaly - same stock as O'Dempsey and O'Dunne

Ó Colghain - (O) or (Mac) Colgan - Co Derry and also of Co Donegal

Ó Coileáin - Collins - Co Limerick and later West Cork - lords of Connello

Ó Cuilleáin - Collins - West Cork - Corca Laoidhe

Ó Concheannain - (O) Concannon - Co Galway - Uí Briúin in Uí Maine, lords of Uí Diarmada

Ó Caoindealbháin - (O) Conlan, Quinlan - Co Meath, princes of Uí Laeghari

Ó Connalláin - Conlon, Conlan or Connellan - Co Galway and Roscommon

Ó Coinghiolláin - Conlon - Co Sligo

Mac Conghaile or Ó Conghaile- (Mac) Conneely - Co Galway (often confused with "Connolly")

Ó Conaill - O'Connell - Co Kerry - chief of Magunihy

Mac Dhomhnaill - Connell and MacConnell - Ulster - the Clan MacDonald

Ó Conghailaigh or Ó Conghaile - (O) Connelly or Connolly - SE Co Galway - Síl nAmnchadha Uí Máine

Ó Conghalaigh or Ó Conghaile - (O) Connolly - Co Fermanagh and Monaghan

Ó Coingheallaigh - Connolly - West Cork

Ó Congalaig - (O) Connolly - Co Dublin/Meath

Mac Canann - Mac Connon - Co Monaghan

Conchobhair - (O) Connor - Co Offaly - descent from Cathaoir Mor

* O'Conor Don, Roe, & Sligo - Connacht, Co Roscommon

* O'Conor Faly - Co Offaly

* O'Conor of Corcomroe - North Clare

* O'Connor Kerry - Co Kerry and also in Keenaught, Co Derry

Ó Maolconaire - (O) (Mul)Conry or Conroy - Co Roscommon

Ó Conraoi - (O) Conry or Conroy - Co Roscommon/Galway - Uí Maine

Mac Conraoi - (Mac) Conroy or King - Co Galway - lord of Delvin of the Two Lakes

Mac Consaidín - MacConsidine - Co Clare - Dal gCais, a branch of O'Brien

Mac Conmhaoil - MacConville or Conwell - Co Armagh (Oriel)

Ó Conbhuidhe - (O) Conway - Co Sligo

Ó Connmhacháin - (O) Conway - Co Mayo - same stock as O'Hara

Mac Connmhaigh or Connmeadha - (Mac) Conway - Thomond

Mac Conmidhe - (Mac) Conway or MacNamee - Co Derry and Tyrone

Mac Congail - Conwell or MacConwell - Co Down

Ó Cuagain - Coogan - Galway/Roscommon - the Uí Maine

Mac Giolla Chomhgaill - (Mac) Cool - Donegal

Mac Cuille or Mac Giolla Chuille - Cooley - Connacht, Roscommon, Clare, Galway.

Ó Cuana - Cooney - Co Tyrone, then north Conacht

Ó Culachain - Coolihan or O'Cuolihan - Co Mayo - the Uí Fiachrach

Mac Corcrain - (Mac) Corcoran - Co Offaly/Tipperary, chief of Clan Ruainni

Ó Corcráin - (O) Corcoran - Co Fermanagh

Mac Cormac - MacCormack - various

Ó Corraidh or Ó Corra - (O) Corr or Corry - Co Tyrone-Fermanagh

Ó Corragáin - (O) Corrigan - Co Fermanagh - same stock as Maguire

Ó Cosraigh - (O) Cosgrave - Co Wicklow, later Wexford

Ó Cosraigh - (O) Cosgrave - Co Galway - Uí Maine

Ó Cosraigh - (O) Cosgrave - Co Monaghan - chiefs of Fir Rois

Mac Oistoghín - (Mac) Costigan - Co Laois - a branch of Fitzpatrick

Mac Oitir - (Mac) Cotter - Co Cork

Mac Cochláin - (Mac) Coughlan - Co Offaly - Dal gCais, chief of Delvin MacCoughlan

Ó Cochláin - (O) Coughlan - Co Cork

Mac Coibheanaigh - Coveney - Co Kilkenny (Ossory) - in Crannagh barony

Mac Giolla Chomhgaill - MacIlhoyle or Coyle - Donegal

Ó Cadhain - Coyne, Kyne or Coen - Co Mayo - the Uí Fiachrach

Mac Ruidhri - MacCrary or MacCreary - Unknown - variant of MacRory?

Craobhach - Creagh - Co Clare - branch of the O'Neills of Clare

Ó Croidheáin - (O) Crean - Co Donegal/Sligo - Cenel Eoghain

Ó Creacháin - (O) Crehan - Co Mayo - the Uí Fiachrach

Ó Criocháin - (O) Crehan or Creighton - Co Tyrone- an Oriel sept

Mac Conchruachan - (Mac)Croghan - Co Roscommon

Mac Criomhthainn - MacCrohan - Co Kerry

Ó Croinin - Cronin - Co Cork

Ó Cruadhlaoich - Crowley - Carbery, Co Cork - Uí Briuin Ai

Ó Cuidighthigh - Cuddihy - Co Cork and Tipperary

Ó Cathaláin - (O) Culhane or Cahalane - Co Limerick - chiefs of Owney Beg

Ó Cuilinn - (O) Cullen - Co Wexford and Wicklow

Ó Cuileannáin - (O) Cullinan - Co Clare

Ó Cuileannáin - (O) Cullinan or Cullen - Co Donegal - of Mullinashee

Ó Cuileannáin - (O) Cullinane - Co Cork - Corcu Liadhe

Ó Coimín - (O) Cummins, Commons - Co Mayo

Mac Coinín - (Mac) Cunneen - Co Mayo

Ó Coinín - (O) Cunneen or Rabbit - Co Offaly and of Thomond

Ó Connagáin and Mac Cuinneagain - Cunningham - Co Sligo - Uí Fiachra

Ó Connagáin and Mac Cuinneagain - Cunningham - Galway/Roscommon - Uí Maine

Mac Toirdhealbhaigh - MacCurley, Curley or Terry - Connacht

Ó Curráin - (O) Curran - SW Connacht - Uí Maine

Ó Corraidhin - (O) Curreen or Curren - Co Leitrim

Mac Curtain - (Mac) Curtin - Co Clare

Mac Cosraigh - MacCusker - Co Tyrone - ernaghs of Clones

Ó Comhraidhe - (O) Corry and Curry - Co Clare

Ó Comhraidhe - (O) Curry - Co Westmeath - chiefs of Moygoish

Ó Dalaigh - (O) Daly - Co Westmeath - Uí Maine branch of the southern Uí Neill

Ó Dorchaidhe - (O) Darcy - Co Mayo and Galway - also of Norman origin

Ó Duibhdabhoireann - (O) Davoren - Co Clare

Ó Deághaidh - (O) Dea - Co Clare - of Inchiquin

Ó Dulchaointigh - (O) Delahunty - Co Tipperary/Kilkenny

Ó Dubhshláine - (O) Delany - Co Laois

Ó Diomasaigh or Dimmussaig - (O) Dempsey - Clanmalier between Co Laois and Offaly

Ó Duineachdha - (O) Dennehy or Denny - Co Cork

Ó Duibhdíorma - (O) Dermond, Dermott, Darby - chiefs of Breadach in Inishowen

Mac Diarmada - MacDermot - Co Roscommon/Sligo - of Mag Luirg (Moylurg)

Ó Duibheamhna - (O) Devany - Co Armagh/Down - ancient chiefs of Ui Breasail

Ó Duibhghiolla - (O) Devilly - Co Galway - the Uí Fiachrach Aidne

Ó Duibhghiolla - (O) Devilly - Co Galway - the Síol Anmchadha

Ó Daimhín - (O) Davin or Devine - Co Fermanagh - lord of Tirkennedy

Ó Doibhilin - (O) Devlin - Co Tyrone and Sligo - lords of Muinter Devlin, Cenel Eoghain

Ó Doibhilin - (O) Devlin - Co Sligo - chiefs in Corran, standard bearer to O'Connor

Ó Dubhuidhe - (O) Devoy or Deevy - Co Laois - 7 Septs of Leix, lord of Cremthainn

Ó Duilleain - Dillon - Co Westmeath, Longford and Mayo - Norman origin

Ó Daighnáin - Dinan - Co Clare and Cork

Ó Duinnín - (O) Dinneen, Dinan - Co Cork - the Corcu Laiodhe

MacDail re Deachair - (Mac) Dockery - Co Roscommon - Clan Dail re deacair (Sil Murray)

Ó Dubhchonna - Doheny or Downey - Co Cork - the Corcu Laoidhe

Ó Dochartaigh - Doherty or Dougherty - Co Donegal - Cenel Conaill, lords of Inishowen

Ó Dubhhláin or Dobhailen - Dolan - S. Roscommon and E. Galway - the Uí Maine

Ó Domhnallain - Donlan - S. Galway - the Uí Maine

Mac Donnchadha - MacDonagh - Co Cork - lords of Duhallow, branch of MacCarthy

Mac Donnchadha - MacDonagh - Co Sligo - lords of Corran, a MacDermot branch

Ó Donnagáin - (O) Donegan - Co Cork - of Muscraige Tri Maighe

Ó Donnagáin - (O) Donegan - Co Westmeath - of Críoch Dungan

Mac Duinnshléibhe - (Mac) Donlevy or Dunleavy - Co Down (Ulidia)

Mac Domhnaill - MacDonnell - Co Antrim - of Clan MacDonald

Mac Domhnaill - MacDonnell - Co Fermanagh - of Clankelly

Mac Domhnaill - MacDonnell - Clare/Limerick (Thomond)

Ó Domhnaill - O'Donnell - Co Donegal - the Northern Uí Neill

Ó Domhnaill - O'Donnell - west Clare and east Galway - the Uí Maine

Ó Domhnalláin - O'Donnellan - Co Galway - the Uí Maine, lord of Clan Breasail

Ó Donnghaile - Donnelly - Co Donegal. later Tyrone - Cinel Eoghain

Ó Donnchadha - (O) Donoghue Mór - Co Cork, Kerry - Eoghanacht Locha Lein

Ó Donnchadha - (O) Donoghue of the Glen - Co Cork. Kerry - the Eoghanacht

Ó Donnchadha - (O) Donohoe - Galway, Cavan and various

Ó Donndubháin - (O) Donovan - Co Limerick, then SW Cork - chiefs of Carberry

Ó Duacháin - (O) Doohan - Co Donegal

Ó Duighlaich - (O) Dooley - Co Westmeath, then NE Tipperary - lords of Fertullagh

Ó Deoráin or O Deoradháin - (O) Doran - Co Laois - 7 Septs of Leix

Ó Deargáin - (O) Dorgan - Co Cork

Ó Dudbhchon - (O) Doughan - Co Cork - Corcu Laoidhe sept

Ó Dubhda - (O) Dowd - Co Mayo and West Sligo - Uí Fiachrach Muaide

Ó Dunlaing - (O) Dowling - Co Laois - 7 Septs of Leix

Ó Dúnadhaigh - (O) Downey - Co Galway - lords of Sil Anmchadha

Ó Dúnadhaigh - (O) Downey - Cork/Kerry/Limerick border - of Luachair

Ó Dubhghaill - Doyle - Co Carlow, Wexford and Wicklow (Norse origin?)

Ó hEidirsceoil - (O) Driscoll - South Kerry, then West Cork - Corca Laoighde

Ó Diubháin - Duane or Devane - Co Galway - erenaghs of Killursa

Ó Dubhthaigh - (O) Duffy - Septs from Co Donegal, Roscommon and Monaghan

Ó Dubhagáin - (O) Duggan - North Cork - Fir Maighe

Ó Dubhagáin - (O) Duggan - Co Galway - in the territory of the Uí Maine

Ó Diubhgeannáin - (O) Duigenan, Deignan, Dignam, ... - Co Roscommon, Leitrim - erenaghs of Kilronan

Ó Doinn or Duinn - (O) Dunn or Dunne - Co Laois - lords of Iregan

Ó Donnchadha - (O) Dunphy - Co Kilkenny - of Iverk barony

Ó Diubháin - Dwane, Devane or Duane - Co Meath - of Knowth

Ó Diubháin - Dwane, Devane or Duane - Co Cork - Corcu Laiodhe

Ó Duibhir or O Dubhuidhir - (O) Dwyer - West Tipperary - of Kilnamanagh

Mac Aodhagáin - (Mac) Egan - Uí Maine territory, then Ormond

Mac Giolla Domhaigh - MacEldowney - Co Derry

Mac Giolla Rua - (Mac) Elroy - Co Fermanagh

Mac Conchradha - MacEnchroe or Crowe - Co Clare

Mac Inneirghe - MacEnery - Co Limerick - Uí Cairbre, same stock as O'Donovan

Ó hAonghuis - Ennis - Co Offaly and Meath - variant of O'Hennessy

Mac Fhiodhbhuidhe - MacEvoy - Co Westmeath, Laois - one of the "7 Septs of Leix"

O'Faodhagáin- Fagan - E. Airgialla (Oriel) - also of Norman origin

Ó Fathaigh - Fahy - Co Galway - Uí Máine, of Pobal Muintir Uí Fhathaigh

Ó Fallamháin - (O) Fallon - Co Roscommon - sept of the Uí Máine (Clann Udach)

Ó Fallamháin - (O) Fallon - Co Meath - of Crich na Cetach

Ó Failbhe - (O) Falvey - Co Kerry - the Corca Duibhne

Ó Fhearghaill or Fergail - (O) Farrell - Co Longford - lords of Annaly

Ó Faircheallaigh - (O) Farrelly or Farley - Co Cavan/Meath

Ó Faracháin - (O) Farren - Co Donegal - Lord of Finross

Ó Fearáin - (O) Fearon - Co Armagh (Oriel) - the Cenél Eoghain

Ó Fiannaidhe - (O) Feeney - Co Sligo/Mayo - sept of the Uí Fiachrach

Ó Fidhne - (O) Feeney - Co Galway/Roscommon

Ó Fithcheallaigh - (O) Fehilly, Field - Co Cork - sept of the Corca Laoidhe

Ó Fiachna - - (O) Feighney, Feeheny, Hunt - Co Roscommon/Sligo - of Síol Muireadhaigh

Ó Fiachra - - (O) Feighry, Feehery, Hunt - Co Tyrone

Ó Fionnaláin - (O) Fenelon - Co Westmeath - chiefs of Delvin (Delbna)

Ó Fiangusa - (O) Fennessy - Co Tipperary/Waterford - chiefs of a district near Cashel

Ó Fearadhaigh - (O) Ferry, Farry - Co Donegal - Cenél Conaill

Ó Fionnachta - (O) Finaghty, Finerty - Co Roscommon - of Síol Muireadhaigh

Ó Fionnachta - (O) Finaghty, Finerty - Co Galway/Roscommon - Uí Maine chiefs of Clanconway

Ó Fionnáin - (O) Finan - Co Mayo - Uí Fiachrach Muaighe chiefs of Coolcarney

Ó Fionn - (O) Finn - Co Sligo - chiefs of Calry

Ó Fionn - (O) Finn - Co Galway - erenaghs of Kilcolgan

Ó Fionn - (O) Finn - Co Monaghan - of Fir Rois

Ó Fionnagáin - Finnegan - Roscommon/Galway

Ó Fionnagáin - Finnegan - Cavan/Monaghan/Louth - a Breifne sept

Ó Finntighearn - Finneran - Co Westmeath? - chiefs of Uí Mella

Mac Fionbhair - Finnevar - Co Leitrim - chiefs of Muintir Greadain

Mac Giolla Mo-Cholmog - Fitz Dermot - Uí Dunchada of Dublin/Kildare

Mac Giolla Phadraig - Fitzpatrick - lords of Upper Ossory (Laois/Kilkenny)

Ó Flaithbheartach - (O) Flaherty - Co Galway - Lord of Moycullen and Iar-Chonnacht

Ó Flannagáin - Flanagan - Roscommon & Offaly

Ó Flannagáin - (O) Flanagan - Fermanagh - Cenel Cairbre of Tuath Ratha (Toora)

Ó Flannagáin - (O) Flanagan - Monaghan - Clan Ceallaigh - the MacDonnels of Clankelly

Ó Flannabhra - Flannery - Co Mayo - the Uí Fiachrach

Ó Flannabhra - Flannery - Co Limerick - the Uí Fidhgheinte, chief of Dal Cairbri

Ó Flaithre - (O) Flattery - Co Down - lords of Lecale, kings of Ulidia

Ó Floinn - (O) Flynn - Co Cork - Muscraige Uí Fhloinn

Ó Floinn - (O) Flynn - Co Cork - Corcu Laoidhe

Ó Floinn - (O) Flynn - Co Roscommon

Ó Flainn - (O) Flynn - Co Antrim

Ó Fhloinn - (O) Lynn - Co Armagh - Clanna Rury, descent from Coll Uais

Ó Fhógartaigh- Fogarty - Co Tipperary, Eliogarty - Dalcassian

Ó Foghladha - Foley - Co Waterford

Mac Giolla na Naomh - Ford - South Connacht

Mac Conshnámha - Forde or MacKinnawe - Co Leitrim - chiefs of Muintir Kenny

Ó Fuaráin - Forde or Foran - Co Cork

Macgiollarnath - Ford - southern Connemara

Ó or Mac an tSionnaigh - Fox - Co. Meath - nickname of a chief of Teffia

Ó Firghil - (O) Friel - Co Donegal - descent from Eoghan, brother of St. Columbcille

Ó Gamhna - Gaffney or Caulfield - Ossory (Laois/Kilkenny)

Mac Carrghamhna - Gaffney or MacCaron - Co Cavan and also Roscommon

Mac Conghamhma - Gaffney or Caulfield - S Galway - Uí Fiachrach Aidhne

Ó Gallchobhair - (O) Gallagher - Co Donegal - Cenel Conaill

Mac Giolla Riabhaigh - Gallery, MacAreavy, Gray - Co. Clare & elsewhere

Ó Gealbháin - (O) Galvin - Co Clare

Ó Gaibhtheacháin - (O) Gahan - Co Mayo - the Uí Fiachrach Muaide

Mag Fhionnáin - (Mac) Gannon - Co Mayo

Ó Gadhra - O'Gara - Co Sligo/Roscommon - chiefs of Luighne Connacht

Mag Fhearadhaigh - (Mac) Garry - Co Roscommon/Leitrim

Ó Gairbhith - (O) Garvey - southern Co Armagh, then Down

Ó Gairbhín - (O) Garvey or Garvin - Co Meath, then Mayo - So. Uí Neill

Ó Garbháin - (O) Garvey or Garvan - Co Cork/Kerry - same stock as O'Moriarity

Mac Gairbhín - (Mac) Garvey - Co Donegal

Mag Aodha - MacGee - Co Westmeath - of Muintir Tlámáin

Mag Aodha - MacGee - Donegal/Tyrone border

Mag Aodha - MacGee - Also of Scottish extraction, with Irish origins

Mag Aonghusa - Magennis or (Mac) Guinness - Co Down - the Dal Araidhe, lords of Iveagh

Mag Eochagáin - (Mac) Geoghegan - Co Westmeath - so. Uí Neill, chiefs of Kinalea

Mag Oireachtaigh - (Mac) Geraghty - Co Roscommon/Galway - Uí Briuin Ai (in Uí Maine)

Mac Giolla Phóil - (Mac)Gilfoyle or Powell - Co Offaly

Mac Giolla Mochuda - MacGillycuddy - Co Kerry - an O'Sullivan Mór branch

Ó Glaimhin - Glavin - Connacht - the Hy Fiachrach

Ó Glesáin - Gleeson or O'Glissane - Tipperary - same stock as O'Donegan

Mag Fhloinn - MacGlinn - Roscommon/Westmeath

Ó Gradaigh - (O) Grady - Co Clare & Limerick - the Dal gCais

Mac Congail - MacGonigle - Co Donegal

Ó or Mac Gormain - Gorman - Co Laois - Uí Bairrche

Ó Gairmleadhaigh - (O) Gormley - Raphoe, Co Donegal - of Cinel Moen (their tribe name)

Mag Shamhradháin - MacGovern / Magauran - Co Cavan - descent of Eochaidh (O'Rourke)

Mac Gabhann - MacGowan or Smith - Co Cavan

Ó Grádaigh - (O) Grady - Co Clare and Limerick

Mac Raith - MacGrath - Co Donegal/Fermanagh

Mac Raith - MacGrath - Co Clare

Ó hUaithnigh - Greene or Green - Co Cork

Ó hUaithnigh - Greene or Green - Co Clare

Mac Glaisin and Mac Giolla Ghlais - Greene or Green - Ulster

Ó Griobhtha - Griffin - Co Kerry and Clare

Mac Carrghamhna. later Ó Gramhna - (O) Growney - Co Tipperary

MagUiginn or MacGuagáin - MacGuigan - Co Tyrone - Cenel Eoghain

Mac Aonghasa or Oengussa - (Mac) Guinness or Magennis - Co Down - the Dal Araidhe

Mag Uidhir - MacGuire or Maguire - Co Fermanagh - rulers of Fermanagh

Ó hÉidin - Hade, Haide, Hayde - Co Galway

Ó hAodhagáin - (O) Hagan or Aiken - Co Tyrone - chiefs at Tullahogue

Mac Céile - MacHale - Co Mayo - also of Welsh origin

Ó haileacháin - (O) Hallahan - Co Cork/Waterford

Ó hAileagáin - (O) Halligan - Co Louth/Armagh (Oriel)

Ó hAllmhuráin - (O) Halloran - Co Clare (Thomond) - same stock as McNamaras

Ó hAllmhuráin - (O) Halloran - Co Galway - Chiefs of Clann Fearghaile

Ó hAghmaill - (O) Hamill - South Tyrone - Cenél Eoghain (Cenél Binnigh)

Ó hÁinle - (O) Hanley or Hanly - Co Roscommon

Ó hAnluain - (O) Hanlon - Co Armagh - lords of Orior

Ó hAnnáin - O'Hannon - Co Clare/Limerick - the Dal gCais

Ó hAnrachain - (O) Hanrahan - Co Clare/Limerick - the Dal gCais

Ó hAnrachtaigh - (O) Hanraghty or Hanratty - Co Armagh and north Co Louth (Uí Meith)

Ó hEaghra or Egra - O'Hara - Co Sligo - lords of Luighne with the O'Garas

Ó hÍr - O'Hare - Co Armagh - Oriel sept of Ó hÉir

Ó hEarcáin - (O) Harkin, Harkan - erenaghs of Clonska, Co Donegal

Ó hAirt - (O) Hart - Co Meath - southern Uí Neill, Four Tribes of Tara

Ó hIongardail - Harrington - Co Cork and Kerry

Ó hArrachtain - Harrington or O'Harraughton - Co Galway

Ó hArtagáin - (O) Hartigan - Co Clare/Limerick - the Dal gCais

Ó hEidedín - Hayden or (O) Headon - Co Carlow

Ó hAodha - Hayes - various counties

Ó hAodha - (O) Hea - Co Cork, Corca Laoidhe

Ó hEilidhe - Healey - Co Sligo

Ó hEaladaighthe - Healey - Muskerry, Co Cork

Ó hEilidhe - (O) Healy - Co Sligo

Ó hÉalaighthe - (O) Healy or Healihy - Co Cork

Ó hÉignigh or O hEicnig - (O) Heany or MacAnenay - Co Fermanagh - Kings of Fermanagh

Ó hEachighearna - Hearne or Ahern - Co Clare - the Dal gCais

Ó hEadroman - (O) Hederman, Hetherman, Heatherman - Co Clare/Limerick, east Cork

Ó hIfearnáin - (O) Heffernan - Co Clare/Limerick - chiefs of Owneybeg

Ó hEigceartaigh - Hegarty - Co Donegal & Derry - Cenel Eoghain

Ó hAichir - (O) Hehir or (O) Hare - Co Clare - Uí Fidhgheinte, lords of Magh Adhair

Ó hAonghusa - Hennessy or Henchy - Co Offaly - lords of Clan Cholgain

Ó hAonghusa - Hennessy - Co Dublian/Meath - chief of Gailenga Beg

Ó hAonghusa - Hennessy - Co Cork - Corca Laoidhe

Ó hInneirghe - Henry or O'Henery - Co Tyrone - chief of Cullentra

Ó hAiniarriadh - Henry - Southeast Ulster

Mac Einri - Henry - North Anthrim/Derry

Ó hOireachtaigh - (O) Heraghty - Co Galway and Mayo

Ó hEisleanáin or Ó hEislin - (O) Heslin - Co Leitrim - a sept of Breffny

Ó hIcidhe - Hickey - Co Clare & N. Tipperary - the Dal gCais

Ó hUigín - Higgins - Co Westmeath, Sligo and Mayo - Southern Uí Neill

Ó hÓgáin - Hogan - Co Clare & Tipperary - the Dal gCais

Ó hUallacháin - (O) Holohan - Co Offaly - of Clan Colgan with the O'Hennessy's

Ó hEoghanáin - (O) Honan - Co Clare and Co Cork

Ó hUaithnín - (O) Honeen, Hoyne, Greene - Co Clare and Tipperary

Ó hOdhráin - (O) Horan - Co Galway and Mayo

Ó hUallacháin - Houlihan - West Munster and Thomond

Mac Aodha or Aoidhe - MacHugh - West Galway - branch of O'Flahertys

Mac Aodha or Aoidhe - MacHugh - North Galway

Mac Aodha or Aoidhe - MacHugh - Co Fermanagh

Ó hAodha - Hughes - Ulster

Ó Urthaile - (O) Hurley - Co Clare & N. Tipperary - the Dal gCais

Ó hUirthile - (O) Hurley - West Cork

Ó hIarlatha - (O) Herlihy or (O)Hurley - Cork

Ó hEidhin - (O) Hynes or (O)Heyne -Galway - Uí Fiachrach Aidne

Mac Giolla Bháin - MacIlwaine or Kilbane - Co Sligo - the Uí Fiachrach

Mac Giolla Riabhaigh - MacIlrea, Kilrea - Co. Sligo & elsewhere

Mac Giolla Ruadh - MacIlroy, McElroy, MacGilroy, Kilroy - various

Mac Giolla Riabhaigh - MacIlwraith - Scottish

Mac an Airchinnigh - MacInerney - Co Clare - son of the erenagh

Ó Cathain - Kane or O'Cahan - East Donegal/Derry - Cenel Eoghain

Caomhanach - Kavanagh - Wexford and Carlow - descent from Donal MacMurrough

Ó Cadhla - (O) Kealy or Kelly - Co Galway - chiefs of Connemara

Ó Caollaidhe - (O) Kealy or Kelly - of Uí Buide, Co Laois

Ó Caollaidhe - (O) Kealy - of Uí Bercháin, Co Kilkenny

Ó Cathain - Keane - Co Galway (or Thomond) - Uí Fiachra Aidne

Ó Cein - Kean - Co Waterford

Ó Cearrnaigh - Kearney - Co Clare - Dalcassian

Mac Cearnaigh - Kearney - Ulster - Cenel Eoghain

Ó Catharnaigh - Kearney - Co Meath & Offaly - chiefs of Teffia

Ó Ciardha - (O) Keary - Co Kildare - the Southern Uí Neill, lords of Carbury

Ó Géibheannaigh - (O) Keaveney - Co Galway - the Uí Maine

Ó Caoimh or Caim - O'Keefe - Co Cork - descent from Art, King of Munster (742-762)

Ó Cianáin - (O) Keenan - Co Monaghan/Louth (Oriel)

Ó Caomháin - (O) Keevan or Kavanagh - Co Sligo - Uí Fiachrach

Ó Céileachair - Kelleher - Co Clare - the Dal gCais

Ó Ceallaigh - (O) Kelly - E Galway & S. Roscommon - Uí Maine (or Hy Many)

Ó Ceallaigh - (O) Kelly - Co Meath - O'Kellys of Breagh

Ó Ceallaigh - (O) Kelly - Co Laois - 7 Septs of Leix

Ó Caellaighe - (O) Kelly - Ossory, Kilkenny/Laois border

Ó Ceallaigh - (O) Kelly - Co Antrim and Down - Cinel Eachrach

Mac Cionath - MacKenna - Co Meath and Monaghan - southern Uí Neill

Ó Cinnéide - Kennedy - Co Clare/Tipperary - the Dal gCais - lords of Ormond

Ó Cionnaoith - (O) Kenny - Co Galway/Roscommon - Uí Maine

Ó Caoinnigh - (O) Kenny or Keeney - Co Leitrim/Donegal - lords of Muinter Kenny

Ó Coinne or O Coinnigh- Kenny or MacKenna - Co Down

Mac Eochaidh - Keogh - S. Roscommon - the Uí Mhaine, lords of Magh Finn

Mac Eochaidh - (Mac) Keogh - West Tipperary

Mac Eochaidh - Keogh - N. Kildare - same stock as the O'Byrnes

Mac Eoghain - MacKeon - Co Sligo/Leitrim

Ó Ciabháin - (O) Kevane or Kavanagh - Co Cork - Corcu Laoidhe

Ó Cadhla - Kiely - Co Clare/Limerick - the Dal gCais

Ó Céirín - (O) Kieran or Kearns - Co Mayo - chiefs of Costello

Ó Ciarain - Kerin or Carey - Co Cork/Clare

Mac Giolla Rua - Kilroy, Gilroy - Co. Clare & elsewhere

Ó Cinnfhaelidh - (O) Kinnealy - Co Limerick

Chennselaig or Cinnsealach - Kinsella - Co Wexford - see MacMurrough

Ó Ciardubháin - (O) Kirwan - Co Galway - one of the Tribes of Galway

Ó Leathlaobhair - (O) Lalor or Lawlor - Co Leix - 7 Septs of Leix

Ó Longáin - (O) Langan or Long - Co Armagh chiefs

Ó Lonagáin - (O) Lanigan - Co Tipperary chiefs

Ó Lorcáin - (O) Larkin - Co Wexford - chief of Fothart

Ó Lorcáin - (O) Larkin - Co Armagh - chief of Farney and West Uí Breasail

Ó Lorcáin - (O) Larkin - Co Galway - the Uí Maine

Ó Lorcáin - (O) Larkin - Co Tipperary - eranaghs of Lorrha

Mac Lochlainn - MacLaughlin - Co Donegal (Inishowen) - the Northern Uí Neill

Ó fLaithbheartaigh - (O) Laverty or Laherty - Co Donegal - lords of Aileach

Ó Limhain - (O) Lavin - Co Roscommon

Ó Laochdha - Leahy - Co Cork - Corca Laoighde

Ó Laoghaire - (O) Leary - Co Cork

Ó Léanacháin - Lenaghan, Linehan or Lenihan - Co Roscommon, Limerick/Tipperary

Ó Leannain - Lennon - Galway, Mayo and Fermanagh

Mac Giolla Mhín - MacLiveen - South Down

Ó Longargain - (O)Lonergan - Co Tipperary

Ó Longain - Long or (O)Langan - Co Armagh

Ó Longaigh - Long - Co Cork

Ó Lochlainn - (O)Loughlin or Lochlain - Co Clare - lord of Corcomroe

Ó Maoilsheachlainn - MacLoughlin or O Melaghlin - Co Meath - of Malachy II (southern Uí Neill)

Mac Lochlainn - MacLoughlin - Co Donegal - northern Uí Neill

Ó Labhradha - (O)Lowry or Lavery - Co Down and Ulster

Ó Lúinigh - (O)Lunney - Co Donegal/Tyrone - Cenel Moen

Ó Loideáin - Lydon, Leyden or (O)Liddane - Co Galway/Mayo

Ó Loinsigh - (O) Lynch - various including chiefs of the Dal Riada

Ó Loinsigh - Lynch - Co Galway - Norman origin, one of the Tribes of Galway

Ó Laighin - Lyons or Lyne - Co Galway and Kerry - Firbolg origin

Ó Liatháin - Lyons or Lehane - Co Cork and Limerick - Uí Fidhgheinte (also a Norman name)

Mac Maolruanaidh - Macarooney - Co Fermanagh

Ó Macdha - (O) Mackey - Co Tipperary - an Ormond sept

Ó Madaidhin or Matudain- Madden - East Galway - Uí Maine tribe

Mac or Mag Aodha - Magee - West and East Ulster (respectively)

Mag Uidhir - Maguire - Co Fermanagh - rulers of Fermanagh

Ó Meachair- Maher or Meagher - North Tipperary

Mac Mathghamha - MacMahon - Co Monaghan - rulers of Oriel (Airgialla)

Mac Mathghamha - MacMahon - Co Clare - the Dal gCais, descent from Mahon O'Brien

Ó Mathghamhna - (O) Mahony - Co Cork - Cenel Aodha, of the Eoghanacht

Ó Máille - O'Malley - Co Mayo - chiefs of Fir Umaille, or Hymalia

Ó Maoil Eoin - Malone - offshoot of the O'Connors of Connacht (?)

Ó Maoileoin - Malone - Co Clare and Wexford - assoc. with the Abbey of Clonmacnois

Ó Mainnín - Mannion or Manning - Co Galway - Pictish origin

Mac Maghnais - MacManus - Co Roscommon - from Maghnais, son of Turlough O'Connor

Mac Maghnais - MacManus - Co Fermanagh - from Maghnuis Maguire, son of Donn Mor

Ó Meadhra - O'Mara or O'Meara - Co Tipperary - chief of Uí Fahy

Mac Giolla Mhartain - Martin or Gilmartin - Co Tyrone - Uí Neill

Ó Miadhachain - Meehan or Meighan - offshoot of MacCarthys of Desmond

Ó Midhir - (O) Meere - Co Clare - Anglo origin

Ó Mealláin - (O) Mellan - Co Tyrone - Cenél Eóghain of Meallanacht

Ó Maoilédigh - (O) Melody - Co Clare/Galway - Corcomroe

MacMeanman -MacMenamin - Co Donegal/Tyrone - Cenél Conaill

Ó Muilleoir - Miller - Co Antrim - Scottish origin, Clan McFarlane

Ó Mochain - Mohan or Moen - Kilmacduagh, Galway and Killaraght, Sligo

Ó Maolmhuaidh - Molloy or Mulloy - Co Offaly - Southern Uí Neill

Ó Maolmhuaidh - (O) Molloy - Offaly - Southern Uí Neill, lords of Fercal

Ó Maoil Aodha - Molloy or Miley - Co Roscommon / East Galway

Ó Maol Dhómhnaigh - Moloney, Mullowney or Maloney - Co Clare - Chiefs of Kiltannon (Dal gCais)

Ó Manachain - Monaghan - East Roscommon - rulers of the 3 Tuathas

Ó Manachain - Monaghan - Co Fermanagh - the Fir Manach based in Lurg

Ó Maonaigh - Mooney - Co Offaly and various other

Ó Móráin - Moran - Co Mayo, near Ballina

Ó Mughráin - Moran - Galway/Roscommon - the Uí Maine, chief of Criffon

Ó Mórdha - (O) More or Moore - Co Laois - leading sept of the 7 Septs of Leix

Ó Murchain - Morgan - Co Managhan - mainly a name of Welsh origin

Ó Muircheartaigh - (O) Moriarty - South Kerry - same stock as O'Donoghues

Ó Muirgheasa - Morris - Co Sligo - the Uí Fiachrach

Ó Maolchathaigh - (O) Mulcahy - Co Tipperyary

Ó Maoldúin - (O) Muldoon - Co Fermanagh - chiefs of Lurg

Ó Maoldúin - (O) Muldoon - Co Clare (Thomond) - the Uí Bloid

Ó Maoldúin - (O) Muldoon - Co Sligo - Uí Fiachrach

Ó‘Maoldoraidh - O'Muldory - Donegal - Tirconnel (MacAlinions)

Ó Maoldomhnaigh - Muldowney - Co Kilkenny

Ó Maolchathail - (O) Mulhall or Mulcahill - Co Laois - descendant of the devotee of (St.) Cathal

Ó Maolchalann - Mulholland - N. Limerick - descendant of the devotee of (St.) Calann

Maoilchiaráin - Mulkerrin, Mulkieran - Roscommon, Galway, Ulster - devotee of (St.) Ciaran

Ó Maolalaidhs - O'Mullally or Lally - Co Roscommon - the Uí Maine

Ó Maolain - Mullan, Mullin(s), Mullen, Mullane - Co Galway - descent from Maolan

Ó Maolain - Mullan, Mullin(s), Mullen, Mullane - Co Derry - followers of the O'Cahans

Ó Maoilédigh - (O) Mulledy - Co Westmeath/Offaly - Ballymaledy

Ó Maolain - Mullins and Mollins - Cork and Monaghan (respectively)

Ó Maolagáin - (O) Mulligan - Co Donegal - chiefs of Tir MacCarthain

Ó Maolchaoine - (O) Mulqueen - Co Clare, Limerick - Dalcassian, from St. Caoine

Ó Maolruanaidh - Mulrooney - Co Fermanagh and in Mayo/Roscommon

Ó Maoilriaghain or Mael Riain- O'Mulryan or Ryan - Co Limerick/Tipperary

Ó Murnain - Murnane - Murnane - Co Limerick

Mac Murchada - MacMurrough - Co Wexford (Hy Chennselaig) - descendant of Murchadh

Ó Murchadha and Mac Murchadha - Murphy - Co Tyrone - the Cenel Eoghain

Ó Murchadha - Murphy - Co Wexford (Hy Felimy)- descendant of Murchadh or Murrough

Ó Muireachaidh - Murray - Roscommon/Galway - the Uí Maine

Ó Muireadhaigh - Murray - West Ireland - including a sept of the Uí Maine

Mac Muireachaidh - (Mac)Murry or MacMorrow - Co Leitrim

Ó Muircheartaigh - Murtagh or MacMurtry - Co Meath

Mac an Fhailghigh - Nally or MacNally - Co Roscommon and Mayo - Norman origin

Mac Con Uladh - MacNally or MacAnally - Co Armagh and Monaghan (S.E. Ulaid)

Mac Conmara - MacNamara - Co Clare - the Dal gCais, rulers of Clancullen

Mac Conmidhe - MacNamee or Conway - Co Derry and Tyrone

Ó Neachtain - (O) Naghten - Co Clare - Dalcassian

Ó Neachtain - (O) Naughton or Naghten - Co Roscommon/Galway - the Uí Maine

Ó Neill- O'Neill - Co Tyrone/Derry/Donegal - the Cenel Eoghain, rulers of Tir Eoghain

Mac an Fhilidh - (Mac) Neilly, Neely - Co Antrim

Mac Aonghasa - MacNiece - Co Antrim

Ó Niallain - Neilan or Neylan - Co Clare (Thomond)

Mac an Airchinnigh - Nerney - Co Roscommon - son of the erenagh

Ó Nuallain - Nolan - Co Carlow - princes of Foharta (Fothairt)

Ó hIonmhaineáin - (O) Noonan - Co Cork

Mac Phaidin - Patterson - Ulster (and Scotland)

Ó Peatáin - Peyton or Patton - Co Donegal - Cenél Moen

Ó Faolain- Phelan or Whelan - Co Waterford - rulers of the Decies

Ó Coigligh - Quigley - Co Mayo - the Uí Fiachrach

Ó Cuill - (O) Quill - Co Cork and Kerry

Mac an Choilgh - MacQuilly or Cox - Co Roscommon

Ó Caoindealbháin - (O) Quinlan or Kindellan - Co Meath - southern Uí Neill

Ó Cuinn - (O) Quinn - Co Tyrone - Cenel Eoghain

Ó Cuinn - (O) Quinn - Co Clare (Thomond) - the Dal gCais

Ó Cuinn - (O) Quinn - Co Antrim - the Glens of Antrim

Ó Cuinn - (O) Quinn - Co Longford - same stock as O'Ferralls of Annaly

Ó Cuirc - (O) Quirke - Co Tipperary - chiefs of Muscraighe Cuirc

Ó Raithbheartiagh - (O) Rafferty - Co Donegal/Sligo

Mac Raghnaill - MacRannall or Reynolds - Co Leitrim - lords of Muintir Eolais

Ó Reachtagáin - (O) Ratigan - Co Roscommon - coarbs of St. Finnen

Ó Riordan - Rearden or (O)Riordan - Co Tipperary/Cork - followers of the Lords of Muskerry

Ó Rodáin - (O) Reddan - Co Clare - stewards to O'Brien and MacNamara

Ó Riagáin - (O) Regan - Co Meath/Dublin - the Four Tribes of Tara

Ó Raogáin - (O) Regan or Reagan - Co Limerick - the Dal gCais

Ó Riada - (O) Reidy - Munster - king of Aradh in the 12th century

Ó Raghallaigh - (O) Reilly - Co Cavan - Uí Briuin Breifne

Ó Maolcraoibhe - Rice - Co Louth/Armagh - also of Welsh origin

Ó Ruanaidh or O Mael Ruanaid - Rooney - Co Down

Ó Roghan - (O) Rogan - Co Down - of Armagh and Iveagh

Mac Ruaidhri - MacRory or MacCrory - Co Tyrone

Ó Ruairc - (O) Rourke - Co Leitrim/Cavan - the Uí Briuin - rulers of Breifne

Ó Ruaidhín - (O) Ruane or Rowen - Co Mayo - the Uí Fiachrach

Ó Ruadháin - (O) Ruane or Rowen - Co Galway - the Uí Maine

Ó Riaghain - Ryan - Co Carlow - chiefs of Uí Drona, also see Mulryan

Ó Scannláin - (O) Scanlan - Munster

Mac Scannláin - (Mac) Scanlan - Louth (Oriel)

Ó Scolaidhe - (O) Scully - Co Westmeath

Ó Scolláin - Scullion or (O) Scully - Co Derry

Ó Seasnáin - Sexton - Thomond (also an English name)

Ó Seanachain- (O) Shanahan - Co Clare - Uí Bloid (Dal gCais)

Mac Seanlaoich - (Mac) Shanly - Co Leitrim - MacShanly of Dromod

Ó Seanáin - (O) Shannon - Carlow/Wexford

Mac Giolla t-Seanáin - (O) Shannon - Co Clare - son of the follower of St. Senan

Mac Searraigh - MacSharry or Foley - Breifne, e.g. northern Leitrim, Sligo

Ó Seachnasaigh - (O) Shaughnessy - Kiltartan, Co Galway - the Uí Fiachra Aidhne

Ó Seaghdha or Segda - (O) Shea - South and East Kerry - Lords of Iveragh

Ó Siodhacháin - Sheehan - Co Limerick/Cork - the Dal gCais

Ó Sirideáin - Sheridan - Co Longford/Cavan

Ó Seiridh or Mac Seiridh - O'Sherry or McSherry - Oriel, e.g. Monaghan and Armagh

Mac an Ghirr - Short, Shortman or Shortel - Unknown

Ó Sluaghain or O’Sluagahadain - Sloan - of Scottish origin

Mac Gabhann - Smith or MacGowan - Co Cavan

Ó Sóchlacháin - (O) Solan, Solahan - Co Mayo

Ó Spealáin - (O)Spillane - Co Tipperary, then Cork & Kerry

Ó Spealáin - Spillane or Spelman - Co Sligo

Ó Suileabháin - (O) Sullivan - Co Kerry - the Eoghanacht - O'Sullivan Mor of Kenmare Bay

Ó Suileabháin - (O) Sullivan - Co Cork - Eoghanacht - O'Sullivan Beare of Beara Peninsula

Mac Suibhne - Sweeney or MacSweeny - Co Donegal - descent of Scottish chief in Argyle

Ó Tarpaigh - (O) Tarpy, Tarpey, Torpey - Co Sligo - lords of Carra

Mac Tighearnáin - (Mac) Tiernan or Kiernan - Co Cavan - chiefs of Teallach Donnchadha

Mac Tighearnáin - (Mac) Tiernan - Co Roscommon - descent of O'Connor

Ó Tighearnaigh - (O) Tierney - Co Mayo - lords of Carra

Ó Tighearnaigh - (O) Tierney - Co Galway, Limerick and Tipperary - Ormond's Fir O'Tyernie

Ó Tuathail - O'Toole - Co Kildare and Wicklow - descent from Tuathal, king of Laigin

Ó Treasaigh - (O) Tracy or Treacy - Co Cork, Galway, Leix (Lords of Slievemargy)

Ó or Mac Tréinfhir - Traynor - Co Meath

Ó Tiobraide - (O) Tubridy - Co Clare

Ó Tuama - O'Twomey or Toomey - Co Cork, and Co Limerick

Mac an Bháird - (Mac) Ward - Co Donegal and Galway

Ó Faolain - Whelan or Phelan - Co Waterford - rulers of the Decies.