Yankton is a city in, and the county seat of, Yankton County, South Dakota, United States. The population was 14,454 at the 2010 census. Yankton is the principal city of the Yankton Micropolitan Statistical Area, which includes the entirety of Yankton County, and which had an estimated population of 22,702 as of July 1, 2015.Yankton was the first capital of Dakota Territory. It is named for the Yankton tribe of Nakota Native Americans; Yankton is derived from the Nakota word I-hank-ton-wan. Yankton is located on the Missouri River just downstream of the Gavins Point Dam and Lewis and Clark Lake and just upstream of the confluence with the James River. The United States National Park Service's headquarters for the Missouri National Recreational River are located in the city. The Human Services Center was established as a psychiatric hospital in 1882 and is on the National Register of Historic Places.