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 was the original capital of Dakota Territory. It is named for the Yankton tribe of Nakota (Sioux) Native Americans. 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 Human Services Center, now a famous landmark, was established as a psychiatric hospital in 1882. It is on The National Register of Historic Places. Yankton is commonly referred to as the 'River City', due to its proximity to the Missouri River and the importance that the river played in the city's settlement and development.