Richland County is a county in the far southeast corner of the U.S. state of North Dakota. As of the 2020 census, the population was 16,529. Its county seat is Wahpeton.

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.