Washburn is a city in southern McLean County, North Dakota, United States. Located along the upper Missouri River, it is the county seat of McLean County. The population was 1,300 at the 2020 census. Washburn was founded in 1882 near the former site of Fort Mandan, winter quarters of the Lewis and Clark Expedition in 1804–1805, near a Mandan village. The town was designated as the county seat in 1883. The city's name honors General Cadwallader C. Washburn.