Kirwan, ó Ciardhubháin A Gaelic surname meaning descendant of Ciardubhán, diminutive of Ciardubh meaning ‘jet-black’. A sept of who were anciently erenaghs of Louth. A sept of Clare. One of the ‘Tribes of Galway’, they appear to have settled in Galway in the reign of Henry VI and from that time they made an important contribution to the city. In 1890 Kirwan was principally found in Dublin, Wexford and Tipperary, and the estimated number of bearers was 2,640. In the United States it is the 8,723rd most numerous surname with an estimated 2,750 bearers.