 The south and west parts of the county are drained by Crow Creek, which discharges into the river at the county's SW corner.The county has a total area of , of which is land and (3.4%) is water.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.