O’Sullivan, ó Súileabháin A Gaelic surname meaning descendant of Súildubhán, which rare personal name meant ‘dark-eyed’. A leading sept, which is said to have originated in Cnoc Rafann now Knockgraffon in the south of Tipperary along the river Suir and forced westwards by Cambro-Norman invaders. Their new home was in the west of Deas Mhumhan (Desmond), on the shores of the bays of Kenmare and Bantry. They divided into several sub-septs : O’Súilleabháin More in the barony of Dunkerron, a branch of this sept was at Cappanacushy. O’Súilleabháin Beare in the territory of Beare now the baronies of Beare and Bantry in Cork. O’Súilleabháin Maol (The leader of the sept was known as: Mac Finghin Dubh). A sept of the Clann Giolla Mochuda, who changed their name to Mac Gillycuddy of Kerry. In 1890, O’Sullivan was the third most numerous surname, the estimated number of bearers was 43,600, and it was the most common surname in Counties Cork (373 births) and Kerry (295 births). In that year the surname was found in every county in Munster. It was also to be found in Dublin, Antrim and Galway. In the United States Sullivan is the 105th most numerous surname with an estimated 222,750 bearers, and O’Sullivan is the 3,853rd most numerous surname with an estimated 8,250 bearers. It is numerous in the state of Connecticut. In England and Wales in 1996 Sullivan was the 241st most numerous surname, and O’Sullivan was the 360th most numerous surname.