Ó Coileáin  Ó Coileáin (Middle Irish: "Ua Cuiléin") is a Modern Irish surname generally belonging to the descendants of the last leading family of the Uí Chonaill Gabra, a sept and small but notable overkingdom of medieval and ancient Ireland, based in western County Limerick. Throughout much of their history the Uí Chonaill Gabra were in turn the leading sept of the greater regional overkingdom of the Uí Fidgenti, considered among the highest ranked princes or flatha in all the Province of Munster. Ó Coileáin/Ua Cuiléin is most commonly anglicized O'Collins and O'Cullane. The surname has also long been found in County Cork, believed largely due to the migration there, probably in the late 12th or early 13th century, of a junior branch of the County Limerick dynasty. It is believed that what is probably a junior branch of the Uí Chonaill kings joined their distant kin the O'Donovan family of the Uí Chairpre Áebda, another great sept of the Uí Fidgenti, in their exodus to Carbery in West Cork between the late 12th and early 13th centuries.