North West Co. fort on west side of Assiniboine river near source of Swan river, in Section 27, Tp. 32, R. 3, West of 2nd Meridian, about 5 miles upstream from Fort Pelly. It was 256 feet long and 196 feet wide. Built in 1780. Attacked by Indians 1782. Was strengthened in 1801 and abandoned in 1805. Harmon was there in 1800 and makes note of the fort being well built and plastered. It is shown on David Thompson's map 1812 (No. 7) and Map of Harmon's Journal (No. 2). It was originally called Fort Tremblant and Poplar Fort but the name was changed in honour of Sir Alexander Mackenzie.