Mulligan, ó Maolacháin A Gaelic surname meaning descendant of Maolachán, from maol, ‘bald’. It is difficult to distinguish any distinct septs. In 1890 Mulligan was principally found in Dublin, Mayo and Monaghan, and the estimated number of bearers was 4,700. In the United States it is the 2,892nd most numerous surname with an estimated 11,000 bearers.