Casper is a city in, and the county seat of, Natrona County, Wyoming, United States. Casper is the second-most populous city in the state after Cheyenne, with the population at 59,038 as of the 2020 census. Casper is nicknamed "The Oil City" and has a long history of oil boomtown and cowboy culture, dating back to the development of the nearby Salt Creek Oil Field. Casper is located in east central Wyoming on the North Platte River.