In 1859, gold was discovered in South Park and a gold rush ensued. Various towns were founded in the gold rush, including Fairplay. Tourists can enjoy the history of the gold rush at South Park City, a town/museum just outside of Fairplay.
In modern times, South Park is best known as an animated television series. Trey Parker, one of the creators of the South Park series, lived for a while in Fairplay. Hence, the television series is probably named after the geographic region.