Tierney, ó Tighearnaigh A Gaelic surname derived from Tighearnach meaning ‘lordly’. A sept of the Cineál Eoghain who were anciently chiefs of Fearnmaigh in the present Donegal. A sept of the Ui Fiachrach who were lords of Ceara, now the barony of Carra in Mayo. A sept of the southern Ui Néill in Westmeath. Note also the immediately preceding surname with which it is confused. In 1890 Tierney was principally found in Dublin, Tipperary and Galway, and the estimated number of bearers was 3,495. In the United States Tierney is the 3,411th most numerous surname with an estimated 11,000 bearers.