Lonergan, Londrigan, ó Longargáin A Gaelic surname meaning descendant of Longargán, diminutive of Lonn garg, meaning ‘strong fierce’. A sept of the Dál gCais who were chiefs in the east of Thuas Mhumhan (Thomond) until after 1318, when they were driven out by the O’Brien and MacNamaras, and settled in Tipperary. The sept produced a number of distinguished ecclesiastics. In 1890 Lonergan was numerous in Tipperary, it was also to be found in Waterford, Kilkenny and Cork. The estimated number of bearers for Lonergan was 2,195, and for Londrigan was 224. In the United States Lonergan is the 9,537th most numerous surname with an estimated 2,750 bearers.