Various claims have been put forward regarding the origin of this clan and it is now generally believed they have some ecclesiastical connection. There were MacMillans in Lochaber in the 12th century and they followed Cameron of Lochiel. Later they migrated to Lawers, in Perthshire, but were driven out in the 14th century. MacMillans were in Knapdale, in Argyll, and in Galloway. The Knapdale family gained in importance and were considered the chief branch. Another prominent family was Dunmore. The Galloway MacMillans were noted Covenanters. The chiefship of the clan is now in the Laggalgarve branch.