Wyoming is a state in the mountain region of the western United States. The state is the 10th largest by area, the least populous and the second least densely populated state in the country. Wyoming is bordered on the north by Montana, on the east by South Dakota and Nebraska, on the south by Colorado, on the southwest by Utah, and on the west by Idaho and Montana. The state population was estimated at 586,107 in 2015, which is less than 31 of the most populous U.S. cities including neighboring Denver. Cheyenne is the state capital and the most populous city, with population estimated at 63,335 in 2015.The western two-thirds of the state is covered mostly by the mountain ranges and rangelands of the Rocky Mountains, while the eastern third of the state is high elevation prairie called the High Plains.