South Dakota is a state located in the midwestern region of the United States. It is the 17th largest state at 78,116 square miles and the 5th least populated with just over 865,000 residents. It became a state simultaneously with North Dakota in 1889. It is bisected by the Missouri River, which divided South Dakota into 2 geographically and socially different halves, "East River" and "West River" are the terms used to describe them among residents.