surnames.ie

Irish surname · 50th most common in 1911

O'Mahony

Also spelt Mahony, Mahoney, O'Mahoney

O'Mahony, often written Mahony or Mahoney, comes from the Irish Ó Mathghamhna, now Ó Mathúna, 'descendant of Mathghamhain', a name meaning 'bear'. The leading family were from Co. Cork, descended from Mathghamhain son of Cian, who died in 1014, and ruled Kinelmeaky on the Bandon river and later the far south-west of the county.

Irish Ó Mathghamhna · Ó Mathúna
1901 census
11,318
#50 · 26 per 10,000
1911 census
11,003
#50 · 25 per 10,000
1926 census
10,581
#35 · 36 per 10,000
Most numerous
Cork
Highest share: Cork

Language & meaning

Meaning & Irish forms

Gaelic Gaelic Irish: a Munster family of the Eóganacht Raithlind, with a separate, smaller family of the same Irish name in east Ulster.[1][2]

Ó Mathghamhna
Modern spelling: Ó Mathúna
“descendant of Mathghamhain”[1][3]
Woulfe's headword. Wikipedia gives Ó Mathúna as the current spelling and Ó Mathghamhna as the traditional one.

The name is built on the personal name Mathghamhain, usually explained as “bear”. The family's eponym was Mathghamhain, son of Cian and grandson of Máel Muad mac Brain, king of Munster.[1][3][4]

Pronunciation

O'Mahony: oh-MAH-hun-ee

Place

Where the O'Mahonys lived

How common the name was in each county, as a share of the population, in the three surviving full censuses of Ireland. Use the buttons to compare years.

Donegal: 0.2 per 10,000 (3 people) Waterford: 45.2 per 10,000 (372 people) Dublin: 10.4 per 10,000 (499 people) Kilkenny: 17.6 per 10,000 (132 people) Carlow: 6.1 per 10,000 (22 people) Limerick: 42.6 per 10,000 (611 people) Louth: 1.7 per 10,000 (11 people) Tipperary: 29.6 per 10,000 (451 people) Roscommon: 1.8 per 10,000 (17 people) Meath: 1.8 per 10,000 (12 people) Wicklow: 2.1 per 10,000 (13 people) Cavan: 0.3 per 10,000 (3 people) Cork: 167.5 per 10,000 (6,583 people) Clare: 27.1 per 10,000 (283 people) Galway: 8.2 per 10,000 (150 people) Mayo: 0.7 per 10,000 (13 people) Sligo: 0.9 per 10,000 (7 people) Leitrim: 0 per 10,000 (0 people) Offaly: 3.7 per 10,000 (21 people) Laois: 8.2 per 10,000 (45 people) Kildare: 10.2 per 10,000 (68 people) Kerry: 97 per 10,000 (1,550 people) Monaghan: 0.3 per 10,000 (2 people) Wexford: 4.3 per 10,000 (44 people) Longford: 1.1 per 10,000 (5 people) Westmeath: 0 per 10,000 (0 people) Tyrone: 0 per 10,000 (0 people) Antrim: 1.1 per 10,000 (52 people) Armagh: 0.5 per 10,000 (6 people) Fermanagh: 0 per 10,000 (0 people) Londonderry: 0.3 per 10,000 (4 people) Down: 0.8 per 10,000 (24 people)
fewerup to 172 per 10,000

Share of each county's census population. 1926 covers the 26 counties of the Irish Free State only.

Highest concentration · 1911

Cork

168 per 10,000

6,583 O'Mahonys · 6.68× the national share

Highest share, 1911

  1. Cork 168
  2. Kerry 97
  3. Waterford 45
  4. Limerick 43
  5. Tipperary 30
  6. Clare 27
  7. Kilkenny 18
  8. Dublin 10

Per 10,000 residents. A concentration index above 1 means the name was commoner there than nationally.

County figures as a table
County190119111926Per 10k 1901Per 10k 1911Per 10k 1926
Antrim2852—11—
Armagh36—01—
Carlow272229769
Cavan334001
Clare271283292242731
Cork6,9026,5836,267172168172
Donegal936100
Down2824—11—
Dublin40549958991012
Fermanagh30—10—
Galway173150140988
Kerry1,6011,5501,441979797
Kildare52688791015
Kilkenny128132121171817
Laois344539688
Leitrim205001
Limerick623611550424339
Londonderry54—00—
Longford552111
Louth161124324
Mayo321331212
Meath15128221
Monaghan624101
Offaly172116343
Roscommon141715122
Sligo877111
Tipperary471451440293031
Tyrone30—00—
Waterford364372344424544
Westmeath2013002
Wexford434473448
Wicklow251334426

Local strongholds in 1911

District Electoral Divisions (300+ residents) where O'Mahonys made up the largest share of the population. In Dromdaleague North, Co. Cork, about one resident in 5 was a O'Mahony.

DEDCountyO'MahonysShare
Dromdaleague NorthCork98 19.1%
AglishKerry46 13.8%
BallybaneCork49 9.1%
MealaghCork56 9.0%
StradballyKerry40 8.6%
TemplemartinCork54 7.7%
KnocksCork28 7.6%
DripseyCork70 7.5%

Origins

Septs & territories

Many Irish surnames were adopted independently by unrelated families. These are the distinct O'Mahony lineages described in the sources.

A surname can point you towards a place. On its own, it cannot establish a pedigree.

Ó Mathghamhna of Cineál mBéice and Fonn Iartharach

Cineál mBéice (the barony of Kinelmeaky) along the River Bandon, and later Fonn Iartharach (Ivagha) in the south-west of the county · Cork

The main family, descended from Mathghamhain son of Cian. Woulfe says they were chiefs of Cineál mBéice and later took control of Fonn Iartharach, 'the western land', a group of parishes in south-west Cork that had belonged to Corca Laoighdhe. Burke describes the sept as holding Hy Eathach or Ivaugh.[1][2][5]

Ó Mathghamhna of Ulidia

Ulidia (east Ulster) · Down

An unrelated family that Woulfe describes as very powerful in Ulidia in the 11th and 12th centuries. He found it still present in Co. Down and elsewhere in east Ulster, but under the anglicised forms Mahon and MacMahon rather than Mahony.[1]

The name over time

History

Descendants of the bear

O'Mahony is an anglicised form of Ó Mathghamhna, written Ó Mathúna in modern Irish, meaning a descendant of Mathghamhain. The personal name means 'bear'. Woulfe lists a range of English spellings, among them O Mahowny, O'Mahony, Mahony, Mahon and Maughan, and Wikipedia adds O'Mahoney, Mahoney and Mahaney as forms used by different branches. Wikipedia names Brodceann as the eldest of Mathghamhain's four sons.[1][3]

Cian, Brian Boru and Clontarf

The family's ancestry runs through Máel Muad mac Brain, who was twice king of Munster and was killed by Brian Boru at the battle of Belach Lechta. His son Cian nevertheless became a close ally of Brian, and later tradition, repeated by the antiquarian John O'Mahony, says he married Brian's daughter Sadb. Several sources suggest Cian lived at Enniskean in west Cork and that the village is named after him. Woulfe says Cian led the forces of Desmond at the battle of Clontarf in 1014, and Wikipedia records that his son Mathghamhain died in that battle.[3][4][1]

Eóganacht roots and Kinelmeaky

The O'Mahonys belonged to the Eóganacht Raithlind, also called the Uí Echach Muman, a branch of the Eóganachta who ruled Munster from the 5th to the 10th centuries. Wikipedia explains that this group divided in the 6th century, and that the Cenél nÁeda, who gave their name to the barony of Kinalea, were one of the two halves. Within it, the Cénel mBéicce, descended from Bécc mac Fergusa who died in 661, later became the O'Mahonys and gave their name to the barony of Kinelmeaky. Woulfe describes Kinelmeaky as an extensive district along the River Bandon.[2][1]

The western land

In a later period the O'Mahonys extended their power into the far south-west of Co. Cork. Woulfe calls this territory Fonn Iartharach, 'the western land', and says it covered several parishes that had earlier belonged to the Corca Laoighdhe. Burke, writing in 1884, describes the O'Mahony sept as possessing Hy Eathach or Ivaugh, the same district, and dates the surname to Mathghamhain, chief in 1014.[1][5]

The Ulster Mahons

Not every family with this Irish name is from Cork. Woulfe records a second Ó Mathghamhna family that was very powerful in Ulidia, the old kingdom of east Ulster, during the 11th and 12th centuries. It survived in Co. Down and nearby counties, but its members came to be known in English as Mahon or MacMahon. So some Ulster MacMahons descend from this Ó Mathghamhna line rather than from the Mac Mathghamhna families of Oriel and Thomond. The confusion runs both ways: Woulfe lists Mahony among the English forms of Mac Mathghamhna too.[1][6]

Soldiers, scholars and rebels

Later O'Mahonys left their mark well beyond Cork. Conor O'Mahony, a Jesuit born in Muskerry in 1594, published his Disputatio apologetica in 1645, a radical argument for full Irish sovereignty that called for a Catholic state under a restored native kingship. Burke records arms allowed in 1712 to John Mahony, a captain in the imperial army, whose father Jeremiah had been a colonel under James II. In the 19th century John O'Mahony, from a minor Catholic landed family at Kilbeheny, became a scholar of Irish and a founder of the Fenian Brotherhood in America.[7][5][8]

Places linked to the name

  • Kinelmeaky (Cineál mBéice), Co. Cork — Barony along the River Bandon named after the Cénel mBéicce, the O'Mahonys' earliest territory.[1][2]
  • Ivagha (Fonn Iartharach), Co. Cork — The 'western land' in south-west Cork that the O'Mahonys later ruled; Burke calls it Hy Eathach or Ivaugh.[1][5]
  • Enniskean, Co. Cork — Village that several sources say was the home of Cian, father of Mathghamhain, and is named after him.[4]

Everyday lives

The O'Mahonys in the census

Who the O'Mahonys were in the 1901 and 1911 censuses (and 1926 where recorded), set against everyone in Ireland in the same census.

O'Mahonys All of Ireland Ireland's figure marked on the O'Mahony bar

Religion, 1911

Catholic +25.4 points vs Ireland
O'Mahonys 99.0%
All of Ireland 73.6%
Church of Ireland −12.4 points vs Ireland
O'Mahonys 0.8%
All of Ireland 13.2%
Presbyterian −10.0 points vs Ireland
O'Mahonys 0.1%
All of Ireland 10.1%
Methodist & other −2.9 points vs Ireland
O'Mahonys 0.2%
All of Ireland 3.1%

Irish language

Spoke Irish, 1901 +12.8 points vs Ireland
O'Mahonys 28.1%
All of Ireland 15.3%
Spoke Irish, 1911 +8.3 points vs Ireland
O'Mahonys 21.8%
All of Ireland 13.5%
Spoke Irish, 1926 · 26 counties +1.5 points vs Ireland
O'Mahonys 15.0%
All of Ireland 13.5%

31 O'Mahonys spoke Irish only in 1901.

Reading & writing

Could read and write, 1901 · aged 15+ −0.9 points vs Ireland
O'Mahonys 79.5%
All of Ireland 80.4%
Could read and write, 1911 · aged 15+ about the same as Ireland
O'Mahonys 85.6%
All of Ireland 85.8%

Family life, 1911

Household size · 2,118 households higher than Ireland
O'Mahonys 5.13
All of Ireland 4.83
Children born per mother · women 45–59 higher than Ireland
O'Mahonys 7.54
All of Ireland 6.46
Children still living −1.7 points vs Ireland
O'Mahonys 78.1%
All of Ireland 79.8%

Commonest occupations

Adults aged 15+, 1901 and 1911 combined.

Farmer1,548
Farmer's son775
Agricultural labourer539
Farmer's daughter455
Farm servant437
General labourer424
Labourer360
Domestic servant293
House keeper237
Farm labourer214

Born outside Ireland

0.8% of O'Mahonys in 1911 gave a birthplace outside Ireland.

England50
United States22
Wales6
Australia & NZ5
India2
Scotland2

Median age: 23 in 1901, 24 in 1911.

Given names

First names among the O'Mahonys

Men and boys

  1. John2,676
  2. Patrick1,700
  3. Michael1,335
  4. James1,210
  5. Daniel921
  6. Denis860
  7. Jeremiah794
  8. Thomas703
  9. Timothy673
  10. William627

Women and girls

  1. Mary2,908
  2. Ellen1,227
  3. Margaret1,171
  4. Bridget851
  5. Kate768
  6. Julia705
  7. Hannah619
  8. Catherine600
  9. Nora437
  10. Annie353

All three censuses combined. Top five in 1926: John, Patrick, Michael, James, Daniel; Mary, Margaret, Ellen, Bridget, Julia.

Spellings

Spellings

This page combines the spellings below, which census enumerators and families used for the same name.

Spelling190119111926Records
Mahony8,0487,0624,995Search
O'Mahony1,2951,9623,244Search
Mahoney1,8271,6831,722Search
O'Mahoney148296620Search

Related forms

  • Mahony — The form without the Ó prefix, listed by Woulfe.[1]
  • Mahoney, O'Mahoney, Mahaney — Spellings Wikipedia associates with different branches of the family.[3]
  • O Mahowny, O Mahown — Older English spellings recorded by Woulfe.[1]
  • Mahon, Maughan — Other anglicised forms of Ó Mathghamhna given by Woulfe; Mahon is also used by the Ulster family.[1]
  • MacMahon — Woulfe notes that the east Ulster Ó Mathghamhna family is sometimes disguised under this name.[1]

Diaspora

The O'Mahonys abroad

Emigration carried the name worldwide. In the 2010 United States census:

SpellingPeopleUS rank
Mahony1,97614965th
O'Mahony73031656th
Mahoney40,397855th
O'Mahoney49543584th

Source: US Census Bureau, 2010 surname file (public domain).

Heraldry

Is there a O'Mahony coat of arms?

Arms belong to particular families, so there is no single O'Mahony crest. Burke's General Armory records arms for the O'Mahony sept of Ivaugh, Co. Cork: a quartered shield with a blue lion rampant on gold in the first and fourth quarters, a lion rampant in counterchanged silver and red in the second, and a chevron between three coiled snakes in the third, with a crest of an armoured arm holding a sword that pierces a fleur-de-lis. Burke notes the same arms were allowed in 1712 to John Mahony, an officer in the service of the Holy Roman Emperor. He gives no motto.[5]

Websites selling a single “O'Mahony family crest” are selling a design, not an inheritance. Arms in Ireland belonged to individuals and their heirs, and the Chief Herald of Ireland still grants arms that way today.

People

Notable people named O'Mahony

  • Conor O'Mahony (1594–1656)
    Cork-born Jesuit whose 1645 Disputatio apologetica argued for full Irish sovereignty.
  • Francis Sylvester Mahony (1804–1866)
    Cork humorist who wrote as 'Father Prout', best known for 'The Bells of Shandon'.
  • John O'Mahony (1815–1877)
    Scholar of Irish who co-founded the Fenian Brotherhood in the United States.
  • Pierce Charles de Lacy O'Mahony (1850–1930)
    Irish nationalist MP and philanthropist.
  • Marion Mahony Griffin (1871–1961)
    Chicago architect and illustrator who helped shape the plan of Canberra.
  • Joseph C. O'Mahoney (1884–1962)
    Democratic US senator for Wyoming, serving 1933–1953 and 1954–1961.
  • Eoin O'Mahony (1905–1970)
    Barrister, councillor and genealogist known as 'the Pope'.
  • Dave Allen (1936–2005)
    Dublin-born comedian, born David Tynan O'Mahony, famed for observational humour.
  • Roger Mahony (born 1936)
    Archbishop of Los Angeles from 1985 to 2011, made a cardinal in 1991.
  • John Mahoney (1940–2018)
    English-born American actor, best known as Martin Crane in Frasier.
  • Peter O'Mahony (born 1989)
    Cork rugby flanker who captained Munster and Ireland and toured with the 2017 Lions.

Questions

Questions about the O'Mahony name

Is O'Mahony an Irish surname?

Yes. O'Mahony is the English form of the Gaelic Ó Mathghamhna. The main family belonged to the Eóganacht dynasty of Munster and ruled districts of Co. Cork, first Kinelmeaky on the River Bandon and later the far south-west of the county. A separate family of the same Irish name lived in east Ulster.[1][2]

What is O'Mahony in Irish?

Ó Mathúna in the modern spelling, traditionally written Ó Mathghamhna. It means 'descendant of Mathghamhain', after the son of Cian who died in 1014 and whose descendants ruled Kinelmeaky and later the south-west of Co. Cork. Woulfe gives older English renderings such as O Mahowny and O Mahown.[3][1][4]

What does O'Mahony mean?

The personal name Mathghamhain means 'bear', so O'Mahony means a descendant of a man named for the bear. The ancestor in question was Mathghamhain, son of Cian and grandson of Máel Muad mac Brain, king of Munster. The same personal name lies behind the separate surname MacMahon.[1][3][4][6]

Are Mahony, Mahoney and O'Mahony the same name?

Yes. All three are English spellings of Ó Mathghamhna, and Wikipedia adds O'Mahoney and Mahaney as forms used by different branches. Woulfe lists older spellings such as O Mahowny and O Mahown, as well as Mahon and Maughan. Mahony can occasionally come from Mac Mathghamhna instead, according to Woulfe.[1][3][6]

Is O'Mahony related to MacMahon?

They share a personal name but are usually separate families. MacMahon normally comes from Mac Mathghamhna, 'son of Mathghamhain', borne by the MacMahons of Thomond and of Oriel. However, Woulfe notes that an east Ulster Ó Mathghamhna family survived in Co. Down under the forms Mahon and MacMahon, and he lists Mahony as an occasional English form of Mac Mathghamhna, so the names do overlap.[1][6]

Is there an O'Mahony family crest or coat of arms?

Not one for everyone of the name. Burke records arms for the O'Mahony sept of Ivaugh in Co. Cork, a quartered shield with lions rampant and a crest of an armoured arm with a sword piercing a fleur-de-lis, which were also allowed in 1712 to an O'Mahony officer serving abroad. These belonged to that family line.[5]

Where does the O'Mahony name come from?

The main family is from Co. Cork. Its first territory was Cineál mBéice, now the barony of Kinelmeaky, along the River Bandon, and they later became lords of the 'western land' in the south-west of the county. Their ancestor Cian is linked by tradition with Enniskean.[1][4]

Where in Ireland is the O'Mahony surname most common?

In the 1911 census the largest numbers of O'Mahonys lived in Cork (6,583), Kerry (1,550), Limerick (611). Relative to population, the name was most concentrated in Cork (168 per 10,000), Kerry (97 per 10,000), Waterford (45 per 10,000).

How common was the O'Mahony surname in Ireland?

11,003 people were recorded as Mahony or O'Mahony or Mahoney or O'Mahoney in the 1911 census of Ireland, making it the 50th most common surname. That is roughly 0.3% of the population, or 1 person in 398.

Looking for a O'Mahony ancestor?

Search every O'Mahony household in the 1901, 1911 and 1926 censuses, with free images of the original forms.

Search records on irishcensus.com

Evidence

Sources

  1. Patrick Woulfe, Ó Mathghamhna, in Irish Names and Surnames (1923)
  2. Wikipedia, Eóganacht Raithlind (2026)
  3. Wikipedia, O'Mahony (2026)
  4. Wikipedia, Cian mac Máelmuaid (2026)
  5. Sir Bernard Burke, The General Armory of England, Scotland, Ireland, and Wales (1884). Entries 'O'Mahony' (the sept of Ivaugh, and the 1712 allowance to John Mahony).
  6. Patrick Woulfe, Mac Mathghamhna, in Irish Names and Surnames (1923)
  7. Wikipedia, Conor O'Mahony (priest) (2026)
  8. Wikipedia, John O'Mahony (2026)
  9. Census of Ireland 1901 and 1911, and Census of Population 1926, National Archives of Ireland. Counts compiled by surnames.ie from the irishcensus.com transcription (dataset 20260831130351). 1926 data © National Archives of Ireland, CC BY 4.0.
  10. Irish forms cross-checked against Gaois surname data (Fiontar & Scoil na Gaeilge, DCU).

How we compile these figures: methodology.