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.