Wahpeton is a city in and the county seat of Richland County, North Dakota, United States. Along the Bois de Sioux River at its confluence with the Otter Tail River, which forms the Red River of the North. The population was 8,007 as of the 2020 census, and was estimated at 8,141 in 2025, making it the 10th most populous city in North Dakota.