Buffalo County, South Dakota: History
As first organized, the county occupied an extensive area, bounded on the north by Canada, southwest and west by the Missouri River, having Montana for a part of its northwest boundary, and comprising a large portion of the "Plateau du Coteau du Missouri", and a part of the Miniwakan or Devil's Lake. Thus, its original boundary also contained a portion of the future North Dakota, which became a separate unit when the Dakota Territory was admitted into the Union in 1889 as two separate states.