Casper (Lakota: Pahášaša Otȟúŋwahe; "Red Hill City") is a city in and the county seat of Natrona County, Wyoming, United States. Casper is the second-largest city in Wyoming, according to the 2010 census, with a population of 55,316. Only Cheyenne, the state capital, is larger. Casper is nicknamed "The Oil City" and has a long history of oil boomtown and cowboy culture, dating back to development of the nearby Salt Creek Oil Field.