McMullan, Macmillan, MacMaoláin A Scottish surname meaning ‘son of the bald or tonsured one’. At one time the Clan Macmillan had possessions near Knap in Argyllshire. In 1890 McMullan was principally found in Antrim and Down, and the estimated number of bearers was 4,840 (including variants). In Scotland in 1995 McMillan was the 67th most numerous surname.