Padraig Mac Giolla-Domhnaigh

Irwin—This name in Ulster is an anglicised form of O' h-Eireamháin. It is confused with Irvine and Irving. The pronunciation of the name in most parts of Ulster is Horan and Oran, and probably the name is a branch of the O'Horan sept that migrated to the county Kerry about six hundred years ago from the borders of the present counties of Derry and Antrim.

Alphabetical Index of Anglicised Surnames in Ireland

See also Woulfe’s Irish Names and Surnames
and O'Hart's Irish Pedigrees