Hennessy, ó hAonghusa
A Gaelic surname meaning descendant of Aonghus, Aonghus a variant of óengus was the young god of Irish tradition. A sept who were lords of Clann Cholgan, a district co-extensive with the barony of Lower Philipstown in Offaly. A sept who were lords of Ui Mac Uais in the barony of Moyfenrath in Meath. A sept who were chiefs of Gailenga Beaga, in Meath/North Dublin. A sept of Dál Cais in Thuas Mhumhan (Thomand). A sept of Moyfenrath (Meath Westmeath). Anglicised as O’Hennessy and sometimes Ennis. In 1890 Hennessey was principally found in Cork, Limerick, Tipperary and Dublin, and the estimated number of bearers was 4,300. In the United States Hennessey is the 4,497th most numerous surname with an estimated 8,250 bearers, Hennessy was the 5,161st most numerous surname with an estimated 5,500 bearers.