Denver officially the City and County of Denver, is the capital and most populous city of the U.S.State of Colorado. It 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 735,538 in 2020, 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