Ó Colgan
Ó COLGAN—I—O Colgan, O Collogan, O Culligan, Colgan, Collogan, Culligan, Quilligan, &c.; 'descendant of Colga'; more anciently Mac Colgan; the name of an old family in Offaly, of the same stock as the O'Connors, O'Dempseys and O'Dunnes; also common in Thomond.
Alphabetical Index to Irish Surnames