Ó Giollagáin
Ó GIOLLAGÁIN—I—O Gillegane, O Gilgan, Gilligan, Gillgan, Gilgan; descendant of Giollagán' (diminutive of giolla, servant, youth); a variant of Ó Giolláin, which see; a scattered surname; formerly most common in Westmeath, Thomond, Galway, Roscommon and Sligo; perhaps sometimes substituted for Ó Gealagáin, which see.
Alphabetical Index to Irish Surnames