Wahpeton is a city in Richland County, in southeast North Dakota along the Bois de Sioux River at its confluence with the Otter Tail River, which forms the Red River of the North. Wahpeton is the county seat of Richland County. The population was 8,007 at the 2020 census. Wahpeton was founded in 1869 and is the principal city of the Wahpeton Micropolitan Statistical Area, which includes all of Richland County, North Dakota and Wilkin County, Minnesota.