Boulder is a home rule city in and the county seat of Boulder County, Colorado, United States. With a population of 108,250 at the 2020 census, it is the most-populous city in the county and the 12th-most populous city in Colorado. Boulder is the principal city of the Boulder metropolitan statistical area, which had 330,758 residents in 2020, and is part of the Front Range Urban Corridor. Boulder is located at the base of the foothills of the Rocky Mountains, at an elevation of 5,430 feet (1,655 m) above sea level. The city is 25 miles (40 km) northwest of the Colorado state capital of Denver. Boulder is a college town, hosting the University of Colorado Boulder, the flagship and largest campus of the University of Colorado system as well as numerous research institutes.