Mac Giollagáin
Mac GIOLLAGÁIN—IV—M'Gillegane, M'Gillgan, M'Illegane, MacGilligan, MacElgan, Gilligan, Gilgan; 'son of Giollagán' (diminutive of Giolla, youth, lad); an Ulster surname, peculiar to Antrim, Derry and Donegal.
Alphabetical Index to Irish Surnames