Irish Surnames: Meanings, Origins and the Top 100 Names in Ireland

Share this ☘️😍

Plenty of people with Irish roots know their surname is Irish. Far fewer know what it means, where it started, or why Granny’s family dropped the O.

I came across this great resource by Barry Griffin on the top Irish surnames in each county. Barry has given me permission to share this data with you today.

This page started as his lists. I’ve now added what the names mean, where they came from, the most common names, and how to start tracing your own.

Jump to:

• What Mac and Ó mean
• How old are Irish surnames?
• Where Irish surnames come from
• How the Ó and Mac went missing
• How the Ó and Mac came back
• The most common Irish surnames
• The top 100 Irish surnames in 1901
• The top surname in each county
• Same name, different county
• How to pronounce tricky Irish surnames
• How to trace your own Irish surname
• Irish surnames FAQ
• More Irish names and words

What Mac and Ó mean

Two little words do most of the work in Irish surnames.

• Mac means “son of”. MacCarthy is Mac Cárthaigh, son of Cárthach.
• Ó means “grandson of”, and more loosely “descendant of”. O’Neill is Ó Néill, descendant of Niall.

Fr Patrick Woulfe explained it in Irish Names and Surnames (1923). A Mac name came from the father of the first man to carry it, and an Ó name from his grandfather. Over time, both came to mean any male descendant.

Not every name comes from a person. Some come from a trade:

• Mac an Bhaird, “son of the bard”, gives us Ward.
• Mac an tSaoir, “son of the craftsman”, was often turned into Carpenter or Freeman.
• Ó Gobhann, “descendant of the smith”, and Mac an Ghobhann, “son of the smith”, often hide under Smith or Smyth.

Ní, Nic and married names

In Irish, a woman does not use Ó or Mac. Woulfe sets out the system:

• Ó becomes Ní, short for iníon, “daughter”. Pádraig Ó Domhnaill’s sister is Máire Ní Dhomhnaill.
• Mac becomes Nic. Eoghan Mac Aodhagáin’s sister is Máire Nic Aodhagáin (Owen and Mary Egan).
• To say “Mrs”, Irish uses Bean, “wife”, with the husband’s name. Mrs John O’Brien is Bean Sheáin Uí Bhriain. Woulfe adds that a married woman kept her own maiden name in Irish.

If you are naming a child rather than tracing a grandfather, my guides to Irish baby names and Irish girl names and how to say them will help.

How old are Irish surnames?

Very old, by European standards.

Britannica says the Gaels were among the first in Europe to adopt hereditary surnames, and dates their start in Ireland to the 10th century. Woulfe agrees. He says surnames came into use gradually from about the middle of the 10th century to the end of the 13th.

The name most often given as the first is Ó Cléirigh, later Clery or Cleary. The Annals of the Four Masters record that Tighearnach Ua Cléirigh, lord of Aidhne, died in 916. John Grenham traces it to cléireach, a cleric.

Early dates in the Four Masters can be a few years out, so treat 916 with some care.

Where Irish surnames come from

“Irish” surnames come from at least five strands. All of them have been in Ireland for hundreds of years.

Gaelic names

Most of the big names are Gaelic: Murphy, Kelly, O’Brien, O’Neill, Ryan, McCarthy. They grew out of the ruling families of medieval Ireland and the people tied to them.

Viking names

The Vikings arrived at the end of the 8th century. Woulfe says Norse families later took surnames “after the Irish fashion”, with Ó and Mac, so they look just like native names.

John Grenham and Fr Woulfe list names with Norse roots, including:

• Doyle, Ó Dubhghaill, “dark foreigner”
• Higgins, Ó hUiginn, from an Irish word for a viking
• McAuliffe, “son of Olaf”
• McBirney, “son of Bjorn”
• McManus, from the Norse name Mánus
• Reynolds, Mac Raghnaill
• Sugrue, Ó Siocfhradha, from the Norse Sigefrith

Norman names

The Normans arrived in 1169. They brought Fitz, from Norman French for “son of” (fils, from Latin filius). That gives us Fitzgerald, Fitzgibbon and Fitzsimons. In Irish, Fitz became Mac, so Fitzgerald is Mac Gearailt.

Other well-known Norman names:

• Burke (de Búrc) comes from William de Burgh, an Anglo-Norman lord who came to Ireland in the late 1100s.
• Power (de Paor) comes from “le Poer”, “the poor”. The family was granted land in Waterford.
• Walsh (Breathnach) simply means “the Welshman”. It was given to Anglo-Norman settlers who came from Wales.
• Barry, Roche, Nugent, Dillon and Prendergast are on Robert Matheson’s list of Anglo-Norman names.

Many Norman families went native and took Irish-style names. The Burkes became MacWilliam, the Barrys of Cork MacAdam, and the Butlers MacPierce. Grenham argues that names like these are simply Irish surnames now. After 850 years, I’d agree.

English and Scottish names

Matheson says many English names came in between the 12th and 18th centuries. Scots had crossed to Ulster since early times. The formal Plantation of Ulster came in the 17th century, and most of its settlers were Scots.

That is why Stewart, Campbell, Scott, Kerr, Graham and Gordon are so common in the north. In 1890 the most common birth surname in Antrim was Smith, and in Down it was Thompson.

How the Ó and Mac went missing

This is the part most people don’t know. Many Irish names lost their prefix, and often their meaning, under English rule.

The laws

Matheson quotes two old statutes:

• 1366: English settlers in Ireland were to use English names and give up the Irish way of naming.
• 1465: Irishmen living among the English in Dublin, Meath, Louth and Kildare had to take an English surname.

The 1465 Act even told them where to find one. It could be a town (Sutton, Trim, Cork, Kinsale), a colour (White, Black, Brown), a trade (Smith, Carpenter) or an office (Cook, Butler).

The clerks

Woulfe says most Irish surnames were put into English between 1550 and 1600, by Anglo-Irish officials. He was blunt about the results: most surnames had been “mutilated by dropping Mac or O'”.

Some of the ways it happened, with Woulfe’s examples:

• By sound: Ó Cobhthaigh became Coffey, Cowhey and Cowhig.
• By translation, right or wrong: Mac Seáin became Johnson. Ó Bradáin became Salmon, and sometimes Fisher.
• By a lookalike English name: Ó hArrachtáin became Harrington, and Ó Lachtnáin became Loftus.

Grenham adds some stranger results, such as Rabbit and Kidney. These were bad translations. Ó Coinín was read as coinín, a rabbit, and Ó Dubháin as dubhán, a kidney.

The result is that some very Irish names now look English. Ward is Mac an Bhaird. Buckley is Ó Buachalla. Most Ryans were once Ó Maoilriain, written O’Mulryan.

How the Ó and Mac came back

You can see the dropped prefixes in the official records. Matheson’s 1890 list has Sullivan, Connor and Reilly, not O’Sullivan, O’Connor and O’Reilly. Oddly, O’Brien and O’Neill kept their O even then. Many families have since taken the O back.

So what changed? The usual answer is the Gaelic revival. The Gaelic League was founded in 1893, and Britannica says Mac has been increasingly revived since the 1890s.

John Grenham, writing on his blog, thinks the change was slower than that. In birth registrations, Mac and Mc names barely moved, from 10.14% of births in 1865 to 10.48% in 1913. O names nearly doubled, but only from 1.67% to 3.2%. He suggests the big return of Mac only came in the early 1920s.

Not every family got its own prefix back. Grenham notes that the O’Gormans were really Mac Gormáin.

The most common Irish surnames

First, a warning. There is no modern official ranking of Irish surnames. The CSO publishes baby first names each year, but not surnames.

The best full official list is still Robert Matheson’s Special Report on Surnames in Ireland. It is based on births registered in 1890. Matheson estimated how many people carried each name, from a population of about 4.7 million.

Meanings below follow Woulfe and other traditional sources. Some are disputed, so read them as “traditionally explained as”.

Rank	Surname	Irish form	Traditional meaning	County most linked	Est. people, 1890
1	Murphy	Ó Murchadha	sea warrior	Cork, Wexford	62,600
2	Kelly	Ó Ceallaigh	war, strife (disputed)	Galway, Roscommon	55,900
3	Sullivan	Ó Súilleabháin	black-eyed (disputed)	Cork, Kerry	43,600
4	Walsh	Breathnach	Welshman	Mayo, Kilkenny, Waterford	41,700
5	Smith	Mac an Ghobhann	son of the smith	Cavan, Antrim	33,700
6	O’Brien	Ó Briain	descendant of Brian Boru	Clare	33,400
7	Byrne	Ó Broin	from Bran, “raven”	Wicklow, Dublin	33,300
8	Ryan	Ó Maoilriain (also Ó Riain)	linked to the name Rian (uncertain)	Tipperary, Limerick	32,000
9	Connor	Ó Conchobhair	high will or desire	Kerry, Connacht	31,200
10	O’Neill	Ó Néill	from Niall, “champion”	Tyrone	29,100
11	Reilly	Ó Raghallaigh	from the personal name Raghallach	Cavan	29,000
12	Doyle	Ó Dubhghaill	dark foreigner	Wexford, Wicklow	23,000
13	McCarthy	Mac Cárthaigh	from Cárthach, “loving”	Cork	22,300
14	Gallagher	Ó Gallchobhair	foreign help	Donegal	21,800
15	Doherty	Ó Dochartaigh	hurtful, disobliging	Donegal, Derry	20,800
16	Kennedy	Ó Cinnéide	helmeted head	Tipperary	19,900
17	Lynch	Ó Loingsigh	having a fleet	Cork, Cavan (top in Westmeath in 1890)	19,800
18	Murray	Ó Muireadhaigh	lord, or mariner	several areas	19,600
19	Quinn	Ó Cuinn	from Conn, “head, sense”	Tyrone	18,200
20	Moore	Ó Mórdha	majestic	Laois	17,700

The top 100 surnames in the 1901 census (Barry Griffin)

Barry Griffin’s count of the 1901 census agrees on the top two: Murphy (56,648), then Kelly (46,481). The numbers in brackets are the people in Ireland with that name in 1901.

These are Barry’s lists as he first shared them with me. Spellings are counted apart, so Smith and Smyth sit separately, and McCarthy turns up twice. His live site now joins Mac and Mc, so a few figures there have shifted a little.

%%TOP100%%

His full maps are free at barrygriffin.com. Type in your surname and you get a map of where it was found.

The top surname in each county

Here is the most common surname in each county in the 1901 census, from Barry’s figures. Beside it is the leading name among 1890 births, from Matheson.

County	Top name, 1901 census (Griffin)	Top name, 1890 births (Matheson)
Antrim	Wilson	Smith
Armagh	Murphy	Murphy
Carlow	Byrne	Murphy
Cavan	Reilly	Reilly
Clare	MacMahon	McMahon
Cork	Murphy	Sullivan
Derry	Doherty	Doherty
Donegal	Gallagher	Gallagher
Down	Johnston	Thompson
Dublin	Byrne	Byrne
Fermanagh	Maguire	Maguire
Galway	Kelly	Kelly
Kerry	Sullivan	Sullivan
Kildare	Kelly	Kelly
Kilkenny	Walsh	Brennan
Laois	Dunne	Dunne
Leitrim	MacGowan	Kelly and Reynolds (level)
Limerick	Ryan	Ryan
Longford	Reilly	Reilly
Louth	Murphy	Byrne
Mayo	Walsh	Walsh
Meath	Reilly	Reilly
Monaghan	MacKenna	Duffy
Offaly	Kelly	Kelly
Roscommon	Kelly	Kelly
Sligo	Brennan	Brennan
Tipperary	Ryan	Ryan
Tyrone	Quinn	Quinn
Waterford	Power	Power
Westmeath	Kelly	Lynch
Wexford	Murphy	Murphy
Wicklow	Byrne	Byrne

Where the columns differ, it’s mostly down to counting. Matheson merged spellings, while Barry keeps most of them apart. In Cork in 1901, Murphy (14,526) edged Sullivan (13,250), partly because the O’Sullivans were counted separately.

No luck? These are 1901 and 1890 counts, and plenty of families have moved since. Barry’s site has the top 50 names for every county if yours isn’t here.

Same name, different county

One Irish name can turn into several English ones depending on where the clerk stood.

• Ó Catháin became Keen in Down, Kane in Derry and Mayo, and Keane in Galway (Grenham).
• Ó Dubhthaigh is Duffy in Monaghan, but Woulfe says it was spelled Duhig in Munster.
• Coffey comes from four different Irish names, says Woulfe.

It works the other way too. Grenham says Murphy arose separately in at least seven places. Two Murphys from Cork and Armagh may share nothing but a name. Sorry to whoever is planning the family reunion.

How to pronounce tricky Irish surnames

These are rough guides. Irish differs between Munster, Connacht and Ulster, so you’ll hear other versions.

Name	Usually said
Meagher	MAR
Geoghegan	GAY-gan
Keogh	KYOH
Coughlan	KOK-lan or KOLL-an, by region
Ó Súilleabháin	oh SOOL-uh-vawn
Ó Ceallaigh	oh KYAL-ee
Mac Cárthaigh	mock KAR-hee
Ó Dochartaigh	oh DOCK-ar-tee

How to trace your own Irish surname

Knowing what a name means is the easy part. Finding your own branch takes records. A lot of the Irish ones are free.

Resource	What you’ll find	Cost
National Archives census search (nationalarchives.ie)	The 1901 and 1911 censuses for all 32 counties. The 1926 census for the 26 counties, released in April 2026. Some fragments from 1821 to 1891.	Free
irishgenealogy.ie	Civil records: births 1864 to 1925, marriages 1845 to 1950, deaths 1864 to 1975.	Free
National Library Catholic parish registers (registers.nli.ie)	Images of baptism and marriage registers from most parishes, mostly up to 1880.	Free, but you browse by parish, not by name
Griffith’s Valuation (askaboutireland.ie)	The 1847 to 1864 property survey, showing who held land and houses.	Has long been free to search
John Grenham’s Irish Ancestors (johngrenham.com)	Maps of where each surname was found in the 1800s and in 1901 and 1911, plus spelling variants.	Five free page views a day. At the time of writing, €7.99 for 24 hours, €11.99 a month or €74.99 a year. His 1926 census search is free.

Prices and coverage change, so check each site before you plan around them.

A few tips

• Start with a place. A parish or townland is worth more than a surname, because the parish registers can’t be searched by name.
• Try every spelling. Grenham points out that after 1899, irishgenealogy.ie indexes names like O’Brien as “OBrien”. Try with and without the O, and both Mc and Mac.
• Expect gaps in 1926. The National Archives is releasing it in phases. Donegal was still being checked at the time of writing, and some people are missing from the transcripts.
• Ask for help. The National Archives runs a free Genealogy Advisory Service by email or in person, and the National Library has a free Family History Service.

Irish surnames FAQ

What is the most common surname in Ireland?

Murphy. It was first in Matheson’s count of 1890 births and first in the 1901 census. Kelly was second both times. There is no modern official ranking.

What does the O’ mean in Irish last names?

It comes from Ó, which means “grandson of” or “descendant of”. Mac means “son of”.

Is there a difference between Mac and Mc?

No. Mc is just a short way of writing Mac, and Britannica says there is no real difference. Mac names are more common in Ulster, partly because many families of Scottish origin settled there from the early 1600s.

What is the oldest Irish surname?

Ó Cléirigh (Clery or Cleary) is the one most often named. The Annals of the Four Masters record the death of Tighearnach Ua Cléirigh in 916. Early annal dates can be a few years out, so treat it as one of the earliest, not a certain first.

Are Walsh, Burke and Fitzgerald Irish names?

Yes, though they arrived with the Normans from 1169. Walsh means “the Welshman”. Many Burkes and Fitzgeralds took Irish-style names, such as MacWilliam and MacMaurice. After eight centuries, they are as Irish as Murphy.

How do I find out where my Irish surname comes from?

Check where it clustered in the 1901 and 1911 censuses. Barry Griffin’s and John Grenham’s maps are the quickest way. Then trace your own line through the free civil and census records.

More Irish names and words

• Top Irish baby names for boys and girls
• Irish girl names and how to pronounce them
• English words that come from Irish
• Irish greetings and what they mean
• Irish slang words you’ll hear at home
• Facts about Ireland

Love this? Save it to your Pinterest board for later.

Share this ☘️😍