Assiniboia, the name of two former districts in western Canada. The first was created in 1811 when land was granted by the Hudson's Bay Company to Lord Selkirk, a Scottish colonizer. Assiniboia included some 116,000 square miles (300,000 km2) in the valleys of the Red and Assiniboine rivers in the region known as Rupert's Land. In 1818 the portion south of the 49th parallel became United States territory (now part of northern North Dakota and Minnesota). When Rupert's Land was transferred to Canada in 1870, Assiniboia was absorbed into the newly formed province of Manitoba.
The second Assiniboia was organized in 1882 as a district of the Northwest Territories. In 1905 the district was absorbed by two newly created provinces—about four-fifths by Saskatchewan, the remainder by Alberta.