The Colorado state capital is DENVER, which is a city of 6 letters. DENVER is the most populous city in the state of Colorado and the capital 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. DENVER is the 22nd most populous city in the United States, the fourth most populous city in the Midwest, and the 19th most populous city in the country.