Sioux County, North Dakota: History
The county was created by proclamation of Governor Louis B. Hanna on September 3, 1914. It was named for the Native American Lakota, whose historic territory included this area. The county government organization was completed on September 12 of that year. The county lies entirely within the Standing Rock Sioux Reservation, forming the northernmost 30 percent of the reservation; the balance of the reservation is in South Dakota. It is the only county in North Dakota that is entirely within an Indian reservation. From 2013 to 2018, Sioux County was included in the Bismarck, ND Metropolitan Statistical Area.