Kiernan, Kieran, ó Ciaráin, A Gaelic surname meaning descendant of Ciarán diminutive of ciar meaning ‘black’. A sept who were lords of Fearmhaigh, Tir Connell, Donegal. A sept who were originally seated in the barony of Imokilly in Cork. Also see Mac Tiernan. In 1890 Kiernan was numerous in Longford, it was also to be found in Cavan, Dublin and Leitrim. The estimated number of bearers was 3,136 (including varients).