The Macmillans are Celts, but whether their first location was in Argyll, Breadalbane, or Lochaber, is a matter of dispute. It is certain they had possessions on both sides of Loch Arkaig. A branch of them appeared in Knapdale, Argyllshire, in the sixteenth century.
Their feudal grant of Knap from the Lord of the Isles was destined to Macmillan “so long as the wave beats on the rock." By marriage, one of their chieftains became allied to the MacNeills, and owned Castle Sweyn. The Chief of the Knapdale branch was called Macmillan of Knap. These Macmillans built the Chapel of Kilmore. In their burial-place there is a high stone cross with the legend in Latin: “This is the cross of Alexander Macmillan."
The Macmillans of Glen Shera, Glen Shira, and others, are descended from a clansman, Gille Maol, who settled at Badokenan on Loch Fyne. The Knapdale succession became extinct, and Macmillan of Dunmore was made Chief. His line also became extinct, and both the Campbells and the MacNeills claimed the lands. The Campbells got possession. The Macmillans of Lochaber were faithful followers of Lochiel. A branch of the clan also settled in Galloway. In later times others went to Arran.
The estates were purchased in 1775 by Sir Archibald Campbell of Inverneil.