Irish Surnames O

A list of Irish surnames beginning with the letter O. Many Irish surnames have a O’ in front in their Irish version, this list is mainly confined to those names where the O’ is commonly used in the English version of the name.

O’Brien

Found in: Clare, Limerick, very widespread.

Origin: Gaelic

Descendents of Brian Boru, High King of Ireland.

O’Callaghan

Variant: Callaghan, Callahan

In Irish: Ó Ceallacháin

Found in: Cork, Limerick, widespread.

Origin: Gaelic

Probably originated from Ceallachan, a 10th century King of Munster.

O’Casey

Variant: Casey

In Irish: O Cathasaigh

Origin: Gaelic

Means “vigilant”.

O’Connell

In Irish: Ó Conaill

Found in: Derry, Galway, Kerry widespread,

Origin: Gaelic

Very old name.

O’Connor

Variant: O’Conor, Conner, Connor

In Irish: Ó Conchobhair,

Found in: Clare, Cork, Kerry, Offaly, Roscommon, widespread.

Origin: Gaelic

Means “hero or champion”; descendents of King Conchobhair of Connacht. .

O’Dea

In Irish: O Deaghaidh

Found in: Clar, Cork, Dublin, Limerick, Tipperary

Origin: Gaelic

O’Donnell

In Irish: Ó Domhnaill

Found in: Donegal.

Origin: Gaelic

Means “world mighty”

O’Donovan

In Irish: Ó Donnabhain

Found in: Cork, Kilkenny

Origin: Gaelic

Two colours in the name: donn meaning “brown” and dubhann “black”.

O’Dowd

Variant: Dodd, Doody, Duddy

In Irish: O Dubhda

Found in: Galway, Mayo, Sligo

Origin: Gaelic

Means “black”.

O’Driscoll

Variant: Driscoll.

In Irish: O hEidersceoil

Found in: Cork

Origin: Gaelic

Means “go between or interpreter”.

O’Dwyer

Variant: Dwyer

In Irish: O Dubhuidir,

Found in: Mayo, Sligo.

Origin: Gaelic

Means “black shirt”.

O’Flaherty

Variant: Flaherty, O’Flaverty. O’Laverty

In Irish: Ó Flaithbheartaigh

Found in: Galway, Mayo

Origin: Gaelic

Very ancient family

O’Gara

In Irish: O Gadhra

Found in: Cavan, Mayo, Sligo.

Origin: Gaelic

Gadhra means “a mastiff ” or “dog”

O’Gorman

Variant: Gorman, Grimes

In Irish: O Gormain

Found in: Clare, Laois, Monaghan.

Origin: Gaelic

O’Grady

Variant: Grady

In Irish: Ó Grádaigh

Found in: Clare, Galway, Limerick.

Origin: Gaelic

Means “illustrious”; part of the Dalcassian sept and so related to the O’Briens.

O’Hagan

Variant: Hagan, Aiken

In Irish: O hAodhagain. Ó hAgain,

Found in: Tyrone, Ulster

Origin: Gaelic

Means “young”.

O’Halloran

Variant: Halloran

In Irish: O hAllmhurain

Found in: Clare, Galway.

Origin: Gaelic

Means “stranger from over the sea”.

O’Hara

In Irish: O hEaghra

Found in: Antrim, Sligo

Origin: Gaelic

O’Hegarty

Variant: Hegerty, Hagerty

In Irish: O hEigceartaigh

Found in: Cork, Derry, Donegal.

Origin: Gaelic

Means “unjust”

O’Higgins

In Irish: O hUigin

Found in: Sligo, Clare, Galway, widespread.

Origin: Gaelic

Means “knowledge or ingenuity”.

O’Keeffe

Variant: O’Keefe

In Irish: Ó Caoinmh

Found in: Cork, Limerick

Origin: Gaelic

Caom means “noble” or “gentle”. Also means “descendent of Caoinmh”, himeself son of Fionghuine, a King of Munster.

O’Leary

Variant: Leary

In Irish: O Laoghaire

Found in: Cork

Origin: Gaelic

Means “calf keeper”

O’Malley

Variant: Melia

In Irish: Ó Máille

Found in: Mayo

Origin: Gaelic

Old and distinguished family. The name is derived from “maglios” an ancient Celtic word meaning “chief”.

O’Meara

Variant: Meara, O’Mara, Mara

In Irish: O Meadhra,

Found in: Tipperary, widespread.

Origin: Gaelic

Means “mirth”.

O’Neill

Variant: Neill, Nihill

Found in: Antrim, Down, Tyrone, widespread.

Origin: Gaelic

Very old and prestigious family. Neill means “champion”.

O’Reilly

Variant: Reilly, Riley, O’Rahilly

In Irish: Ó Raghailligh

Found in: Cavan, widespread

Origin: Gaelic

Ragheallach means “gregarious race”

O’Riordan

Variant: Riordan, Reardon.

In Irish: O Riordáin

Found in: Cork, Tipperary.

Origin: Gaelic

Means “royal bard”.

O’Rourke

Variant: Roark, Rooke, Rourke, Rorke

In Irish: Ó Ruairc

Found in: Cavan, Leitrim.

Origin: Norse

Originates from the Norse-Viking name Hrothrekr, who married into the Irish.

O’Shaughnessy

Variant: Shaughnessy

In Irish: O Seachnsaigh

Found in: Clare, Galway, Limerick.

Origin: Gaelic

O’Shea

Variant: Shea, Shee

In Irish: Ó Séaghdha, Ó Sé

Found in: Kerry, Kilkenny.

Origin: Gaelic

Means “stately or majestic” and also “dauntless”. One of the merchant families of Kilkenny.

O’Sullivan

Variant: Sullivan

In Irish: Ó Súileabháin

Found in: Cork, Kerry, Tipperary.

Origin: Gaelic

Means “one-eyed” or “hawk-eyed”.

O’Toole

Variant: Toal, Tool, Toole, Toohill, Twohill.

In Irish: Ó Tuathail

Found in: Kildare, Wicklow, widespread.

Origin: Gaelic

Descendents of Tuathal, a 10th century King of Leinster. Means “mighty or prosperous people”

Article updated: March 31, 2017 | Image Credits

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10 Comments

  • Frank Hughes says:

    My grandmothers maiden name was O’Philemy from the Strabane area, I think. They came to Scotland in about 1900. O’Philemy is not on your list. I’d like to know more about the name and most likely associated places. Can you help me, please?

  • Bayram says:

    What does the letter “O ” stand for before surnames( what does it mean) thanks

  • Carol says:

    I cannot find mention my late grandmother’s surname which was O’Hore, not sure of the spelling though. Can you help please.

  • John Shannon says:

    Why do you listings just go to the letter ‘O’ where are all the names from P to Z/ … in my case ‘S’

  • Stephen Mulvey. says:

    Hi.
    I have looked at your list of surnames,but I can’t find mine,Mulvey. My father was Irish from Tipperary,so I Am presuming it was an Irish surname,appreciate it if you had any information  at all about its origins. 
    Regards
               S Mulvey.

    • Katherine says:

      It is indeed an Irish surname, and not an uncommon one. I don’t know a lot about it, but it is a name of Gaelic origin, in Irish it would be Ó Maoilmhiadhaigh – which I bet looks kind of unpronounceable! ‘Mwale (rhymes with ale) – vade- ig’ would be there or thereabouts. I see from a quick search online that there is a general consensus that the comes from the Irish ‘Maidach, meaning honourable. I kind of don’t think that’s quite right. My Irish isn’t brilliant, but I’ve not heard that word – which definitely doesn’t mean it does not exist! Maybe it’s old Irish, or maybe just unknown to me.

      The fist part ‘Maoil’ means ‘follower of’, so I’d be inclined to go for the second part as being a person’s name, a leader of some kind. Maybe his name meant honourable, or perhaps he was an honourable person and that’s where this came from.

  • bear32ie says:

    I notice you have Dwyer/O’Dwyer name coming from Mayo/Sligo but it is from Kilnamanagh in Tipperary. I am a Dwyer from this part of the country. The biggest number of Dwyer/O’Dwyer (900+) families currently live there. This is where the Dwyer/O’Dwyer castles are also located, which were destroyed during the Cromwellian settlements.

  • Mariano Driotes says:

    My last name is Driotes, some how it has been deformed, according to our family records, our grand grand father came from Europe so the last known last name was Driottiz or Driotez somebody can help me?

  • lgfiggins says:

    Our name in the Gaelic was originally O’ Faodhagain.  Translates into Fagan here. Somewhere along the line it changed to the “Figgins” of today. Please, where do I start research on the name? Are there websites, books or libraries in Ireland that you could recommend?  Thank you.

  • Catherine O'Haire says:

     I notice with some dismsy that O’Haire is not listed! I can only presume that it si a derivation of  another. In gaelic it is Mac an Aodhaoire son of shepherd! How did it become O’Haire

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