Costello

Origin of the Costello Name

The Costello family holds a singular distinction in Irish history: they were among the first Norman families to abandon their original French surname and adopt a Gaelic-form Mac name — doing so as early as the mid-thirteenth century, within a few generations of the Norman arrival in Ireland. This was a deliberate act of cultural identification, and it made the Costellos a landmark in the story of how Norman settlers became Irish.

The family's Norman origin was as de Angulo — anglicised in various ways as Nangle, de Nagle, or simply Angulo — one of the Anglo-Norman families who arrived in Ireland in the 1170s and 1180s following the initial conquest. They received lands in Connacht, where the Norman penetration was less complete than in Leinster and Munster, and established themselves in the territory between Lough Conn and the Roscommon border in what is now east Mayo.

Around 1250, a member of the family named Jocelyn — in Irish Oisdealbh — had a son who took the Gaelic patronymic Mac Oisdealbhaigh: "son of Oisdealbh." This patronymic became the family's hereditary surname. The anglicised form Costello derived from the Irish through the natural softening of sounds — Mac Oisdealbhaigh contracted and anglicised to Costelloe and then Costello. The barony of Costello in east Mayo still commemorates the family today.

Territory — the Barony of Costello

The Costello family's territorial base was Tirmaine — sometimes written Tír Mhaine — in east County Mayo. Their territory occupied the eastern fringe of Connacht, bounded by Lough Conn to the west, the Roscommon border to the east, and the south Mayo lowlands. This was a landscape of drumlins, small lakes, and bogland — productive enough for mixed farming but also isolated enough to maintain a certain political independence from the larger powers of Connacht.

The barony of Costello in east Mayo preserves the family's name on the modern map. It is one of a handful of baronies in Ireland named after the Gaelic-form surname of a Norman family — an unusual circumstance that reflects the depth of the Costello identification with their Mayo territory. The towns of Ballaghaderreen and Charlestown now mark the eastern edge of the old Costello country.

The Costello territory lay within the broader sphere of influence of the Mayo O'Malley and Bourke families, and the Costellos navigated the complex politics of Connacht as a significant but not dominant family. They held their barony through the medieval period while the larger Connacht powers — the O'Connors, the O'Malleys, the MacWilliam Bourkes — contested the province around them.

Costello Through Irish History

The medieval period

The Mac Oisdealbhaigh chiefs appear in the Annals as lords of their Connacht territory from the thirteenth century onwards. Their history is woven into the complex political fabric of medieval Mayo, where Gaelic dynasties, Gaelicised Norman families, and the remnants of the original Norman settlement all competed for land and influence. The Costellos were part of the Gaelic political world — attending assemblies, making alliances by marriage, and participating in the cycles of raiding and negotiation that characterised Connacht politics.

By the late medieval period, the family was sufficiently established that their territory had given its name to a formal barony — an administrative unit recognised by the English crown as well as by Gaelic customary usage. This dual recognition — as Lords of Tirmaine in the Gaelic system and as identifiable proprietors in the emerging English administrative order — gave the Costellos a degree of stability that some smaller septs lacked.

The Cromwellian era and its consequences

The Cromwellian settlement of the 1650s, following the Confederate and Williamite wars, was catastrophic for Catholic landowning families throughout Ireland. The Costello family, like most of the old Connacht gentry, lost whatever land they held under the legal title of the pre-war period. The "To Hell or to Connacht" policy — by which Catholic landowners from other provinces were offered lands west of the Shannon in exchange for their eastern properties — brought new settlers into the midlands while leaving Connacht's existing Catholic families under pressure.

The surviving Costello families became tenant farmers and labourers in their ancestral territory — a profound social demotion from their former status as lords of the barony. By the eighteenth century, the family were part of the broad Catholic tenant class of east Mayo, maintaining a cultural memory of their former status while legally occupying a subordinate position in the new order.

Costello in the Diaspora

The Costello diaspora is primarily a product of the post-Famine emigration from Connacht. County Mayo was among the most severely affected counties during the Great Famine of 1845–1852 — the population of Mayo fell by approximately 30 percent through a combination of mortality and emigration, and continued falling through successive waves of emigration throughout the nineteenth century. East Mayo, the ancestral Costello territory, was not spared.

Mayo emigrants in this period went overwhelmingly to New York, which was the primary port of entry for Connacht emigration. The established Irish communities of lower Manhattan and the emerging neighbourhoods of the Bronx received large numbers of Mayo families from the 1840s onwards. The Costello name appears across the New York Irish community from the mid-nineteenth century, and has remained a recognisable name in the city's Irish-American life.

The most famous American Costello was Lou Costello (1906–1959), the comedian of the Abbott and Costello comedy duo. His family's Italian-American background — his father was from Calabria — produced a coincidental surname that carries no Irish ancestry, illustrating how the same anglicised form could arrive from entirely different origins in the American immigrant context.

Researching Costello Ancestry

East County Mayo is the primary research territory for Costello ancestry. The barony of Costello — the civil parishes of Kilcolman, Kilmovee, Killtullagh, and surrounding areas — is where the densest concentration of Costello families lived in the nineteenth century. Civil registration records from 1864 and Catholic parish registers provide the essential record base.

Key sources

IrishGenealogy.ie — civil birth, marriage, and death records from 1864. The Swinford and Claremorris civil registration districts cover most of the ancestral Costello territory in east Mayo.

RootsIreland.ie — Mayo Catholic parish registers. The parishes of Kilmovee, Kilcolman, and surrounding east Mayo parishes have registers going back to the early nineteenth century.

Griffith's Valuation (1847–1864) — Costello appears extensively in east Mayo parishes. The barony of Costello itself is the starting point; the specific townland address from Griffith's is essential for accessing earlier records.

Mayo County Library and Local Studies — The Mayo County Library in Castlebar maintains local history resources including estate papers, tenant lists, and local historical studies relevant to east Mayo families. The Costello barony is well-documented in local antiquarian literature.