Yankton is a city in Yankton County, South Dakota, United States. The population was 13,528 at the 2000 census. It is the county seat of Yankton County. 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. A famous landmark is the Human Services Center it 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 close proximity to the Missouri River, and the importance that it played in the city's settling and subsequent development.