Thornton An English surname of local origin. However Mac Giolla Domhnaigh states that in most parts of south Connacht and North Munster it is the anglicised form of Draighneain, a sept of south Galway. In 1890 Thornton was principally found in Gaway, Dublin and Mayo, and the estimated number of bearers was 2,420. In the United States it is the 354th most numerous surname with an estimated 85,250 bearers. In England and Wales in 1996 it was the 302nd most numerous surname.