City and County of Denver First most populous Colorado city Second most populous Colorado county Denver ( /ˈdɛnvər/) is the capital and the most populous city of the U.S. state of Colorado. As Denver County, it is the second most populous county in Colorado after El Paso County, which surpassed Denver County as of the 2010 Census. Denver is a consolidated city-county, 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. The Denver downtown district is located immediately east of the confluence of Cherry Creek with the South Platte River, approximately 12 miles (19 km) east of the foothills of the Rocky Mountains. Denver is nicknamed the Mile-High City because its official elevation is exactly one mile (1.6 km) or 5,280 feet (1,609.344 m) above sea level, which is defined by the elevation of the spot of a benchmark on the steps of the State Capital building. The elevation of the entire city ranges from 5,130 to 5,680 feet, and, some sources, such as the GNIS data and the National Elevation Dataset mark the elevation at 5,278 feet, which is reflected on various websites such as that of the National Weather Service. The 105th meridian west of Greenwich passes through Union Station and is the temporal reference for the Mountain Time Zone. The population of Denver was 600,158 according to the 2010 census which ranks it as the 27th most populous U.S. city. The 10-county Denver-Aurora-Broomfield, CO Metropolitan Statistical Area had an estimated 2009 population of 2,552,195 and ranked as the 21st most populous U.S. metropolitan statistical area and the 12-county Denver-Aurora-Boulder Combined Statistical Area had an estimated 2009 population of 3,110,436 and ranked as the 16th most populous U.S. metropolitan area. Denver is the most populous city within a 500-mile (800 km) radius and the second-largest city in the Mountain West and Southwest after Phoenix. Denver is the most populous city in the Front Range Urban Corridor, an urban region stretching across 18 counties in two states. The population of the Front Range Urban Corridor was estimated to be 4,328,406 in 2009.