Situated in the western north-central US, South Dakota ranks 16th in size among the 50 states.
The state has a total area of 77,121 sq mi (199,730 sq km), comprising 75,896 sq mi (196,715 sq km) of land and 1,164 sq mi (3,015 sq km) of inland water. Shaped roughly like a rectangle with irregular borders on the E and SE, South Dakota extends about 380 mi (610 km) E-W and has a maximum N-S extension of 245 mi (394 km).
South Dakota is bordered on the N by North Dakota; on the E by Minnesota and Iowa (with the line in the NE passing through the Bois de Sioux River, Lake Traverse, and Big Stone Lake, and in the SE through the Big Sioux River); on the S by Nebraska (with part of the line formed by the Missouri River and Lewis and Clark Lake); and on the W by Wyoming and Montana.
The total boundary length of South Dakota is 1,316 mi (2,118 km). The state's geographic center is in Hughes County, 8 mi (13 km) NE of Pierre. The geographic center of the US, including Alaska and Hawaii, is at 44°58′ N, 103°46′ W, in Butte County, 17 mi (27 km) W of Castle Rock.