What the historical record says
Mulligan anglicises the Gaelic Ó Maolagáin, from maol, "bald" or "tonsured," in the sense of a devotee. The sept originated in County Donegal, in the country of Tír Conaill, and from there dispersed south and east into Fermanagh, Monaghan and Mayo. The Ó prefix was almost entirely dropped in the anglicised form, and the name is today most numerous across the south Ulster and north Connacht counties, occasionally also rendered Molyneux.
Recorded Gaelic root: Ó Maolagáin
Strongest county signals
- Leitrimprocessed surname/place signal
What this evidence can—and cannot—prove
Census clustering can show where a surname appeared strongly at a historical point in time. It cannot identify your exact ancestor, prove a clan relationship, or assign a coat of arms. Use it as a source-backed starting point alongside family records and parish research.