Yankton is a city in, and the County seat of, Yankton County, South Dakota, U.S. 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 22,662 as of July 1, 2017. Yankton was the first capital of Dakota Territory. It is named for the Yankton tribe of Nakota (Sioux) Native Americans; Yankton is derived from the Nakota word I-hank-ton-wan.