| Gaelic form | Ó Ceallaigh |
| Meaning | Descendant of Ceallach |
| Etymology | ceallach — "bright-headed," "warlike," or "frequenting churches" |
| Province | Strongest in Connacht; present across all four |
| Core counties | Galway, Roscommon, Meath, Wicklow, Derry |
| Rank in Ireland | No. 2 — second most common surname in Ireland |
| Variant spellings | O'Kelly, Kelley, Kiely, Queally |
Kelly has been the second most common surname in Ireland for as long as reliable records exist. It is one of the most recognisable Irish names in the English-speaking world, carried across the Atlantic, Pacific, and Indian Ocean by the waves of Irish emigration that reshaped the nineteenth and twentieth centuries.
The name derives from the personal name Ceallach, whose exact meaning has been debated by scholars for centuries. The most widely accepted interpretations include "bright-headed," "warlike," or "frequenting churches" — the last from ceall, an Old Irish word for a church or monastic cell. Any of these might explain why the name was popular: Ireland was simultaneously a culture of warriors and of monks, and a personal name that could suggest either quality would have been well used.
As a surname, Ó Ceallaigh (grandson/descendant of Ceallach) arose independently in at least five different parts of Ireland, which is part of why Kelly is so geographically widespread. Unlike Murphy — which has a clear dominant sept in Leinster — Kelly has multiple septs of roughly equal historical significance.
Kelly is one of a small number of Irish surnames found in significant concentrations across all four provinces. The main septs, by province:
The most historically prominent Kelly sept were the Ó Ceallaigh of Uí Maine — a Connacht kingdom covering parts of east Galway and south Roscommon. They were kings of Uí Maine and maintained power through the medieval period. The territory of Uí Maine, sometimes called Hy Many, was one of the ancient kingdoms of Connacht, and the O'Kellys were its ruling family for centuries.
The O'Kelly chiefs are commemorated in the Book of Uí Maine (also called the Book of the O'Kellys), a fourteenth-century manuscript that is one of the most important surviving sources for Connacht history and genealogy. Galway remains the county most associated with the Kelly name.
A distinct Kelly sept held territory in County Meath and adjacent counties. A further Leinster sept was established in County Wicklow. Both are independent of the Connacht O'Kellys.
County Derry (Londonderry) had its own Ó Ceallaigh presence, again independent of the Connacht or Leinster septs. This Ulster Kelly lineage accounts for the name's significant presence in the north.
While less prominent than in the other provinces, Kelly is present throughout Munster. Some Munster Kellys descend from a sept in Tipperary; others represent northward and westward migration from the Leinster septs.
The Connacht O'Kellys were among the most powerful ruling families of medieval Ireland. As kings of Uí Maine, they controlled a significant Connacht territory and maintained royal status through the Norman period — an achievement many Gaelic dynasties failed to manage. The O'Kelly chiefs patronised the arts and scholarship: the Book of Uí Maine, commissioned in the fourteenth century, contains some of the most important surviving manuscripts of Irish poetry and genealogy.
The O'Kellys remained lords of their Connacht territory until the Elizabethan conquest of Connacht in the late sixteenth century, when the systematic replacement of Gaelic landholders with English settlers ended their political power, though not their cultural presence.
The O'Kelly chiefs, like other Gaelic ruling families, lost their territorial authority during the Elizabethan and Cromwellian plantation periods. Many lesser Kelly families — those who had not held the chief's title — were able to remain on the land as tenants under the new order, which may partly explain why Kelly survived in high numbers when many smaller Gaelic surnames dwindled.
Galway and Roscommon — the heartland of the O'Kelly territory — were among the most severely affected counties during the Great Famine of 1845–1852. County Roscommon lost approximately a quarter of its population; County Galway lost a similar proportion. The Famine-era emigration from these counties sent large numbers of Kellys to America, Britain, and Australia, seeding the Irish diaspora communities that would carry the name through the twentieth century.
Kelly is among the most common Irish-derived surnames in the United States, Australia, Canada, and the United Kingdom. The American Kelly community is deeply rooted in the urban Catholic culture of the northeast — New York, Boston, Philadelphia, Chicago — built by Famine-era and post-Famine emigrants.
Grace Kelly, Princess of Monaco, is perhaps the most globally recognised Kelly of the twentieth century. Born in Philadelphia to an Irish-American family, her father Jack Kelly was a self-made millionaire whose own father had emigrated from County Mayo. Her marriage to Prince Rainier III of Monaco in 1956 was one of the most watched events of the decade.
Ned Kelly, the Australian bushranger executed in Melbourne in 1880, is among the most complex and contested figures in Australian history. Born in Victoria to Irish immigrant parents — his father was from County Tipperary — Ned Kelly became a symbol of Irish-Australian resistance to British colonial authority. His last stand at Glenrowan, wearing home-made iron armour, remains one of the most dramatic episodes in Australian history.
In American politics, the Kelly name has been prominent in Irish-Catholic political machines, particularly in Philadelphia and New York, where ward bosses and city councillors named Kelly were a familiar feature of twentieth-century urban life.
Kelly presents the same core research challenge as Murphy: it is too common and too geographically widespread to narrow without county of origin. Establishing where your Kelly ancestor was from — ideally to the townland level — is the single most useful step before searching Irish records.
IrishGenealogy.ie — civil birth, marriage, and death records from 1864, free and searchable by name and county.
RootsIreland.ie — Catholic parish registers, which predate civil registration and are essential for ancestors born before 1864.
Griffith's Valuation (1847–1864) — land survey naming every head of household, searchable free at Ask About Ireland. Use this to identify Kelly families in specific townlands within a county.
The Book of Uí Maine — for those researching the Connacht O'Kellys specifically, this fourteenth-century manuscript is a primary source for the lineage. It is held by the Royal Irish Academy and partially digitised.
DNA — as with Murphy, DNA testing (particularly AncestryDNA with ThruLines) can connect you with other Kelly researchers and help identify which sept lineage you descend from.
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