Denver (), officially the City and County of Denver, is the capital and most populous city of the U.S. State of Colorado. Denver is located in the South Platte River Valley on the western edge of the High Plains just east of the Front Range of the Rocky Mountains. With an estimated population of 727,211 in 2019, Denver is the 19th-most populous city in the United States, the fifth-most populous state capital, and the most populous city located in the Mountain states. The metropolitan area surrounding Denver represents a majority of the population and economic activity in the Front Range region, the area where an estimated 85% of Colorado's population lives. The Denver downtown district is immediately east of the confluence of Cherry Creek and the South Platte River, approximately east of the foothills of the Rocky Mountains. Denver is named after James W. Denver, a governor of the Kansas Territory. It is nicknamed the "Mile High City" because its official elevation is exactly one mile () above sea level. The 105th meridian west of Greenwich, the longitudinal reference for the Mountain Time Zone, passes directly through Denver Union Station.