Casper is 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 53,569. 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.Casper is located in east-central Wyoming at the foot of Casper Mountain, the north end of the Laramie Mountain Range, along the North Platte River. Interstate 25 approaches Casper from the North and East and is the main avenue of transportation to and from the city. The towns immediately adjacent to Casper are Mills, Evansville, Bar Nunn, and Mountain View. Unincorporated areas include Allendale, Dempsey Acres, Red Buttes, Indian Springs, and several others.