Corson County lies on the north line of South Dakota. Its north boundary line abuts the south boundary line of the state of North Dakota. The Missouri River flows south-southeastward along its eastern boundary line. The county terrain consists of semi-arid rolling hills. A portion of the land is dedicated to agriculture. The Grand River flows eastward through the central part of the county to discharge into the river, and Standing Cloud Creek flows eastward through the county's lower SW area. The terrain generally slopes to the east and south; its highest point is near its NW corner, at 2,582' (787m) ASL.