City of Boulder Eleventh most populous Colorado city Boulder is the county seat and most populous city of Boulder County and the 11th most populous city in the U.S. state of Colorado. Boulder is located at the base of the foothills of the Rocky Mountains at an elevation of 5,430 feet (1,655 m). The city is 25 miles (40 km) northwest of Denver. The United States Census Bureau reported that in 2010 the population of the City of Boulder was 97,385, while the population of the Boulder Metropolitan Statistical Area was 293,161. Boulder is famous for its status as one of the most liberal cities in Colorado, its colorful Western history, being a choice destination for hippies in the late 1960s, and as home of the main campus of the University of Colorado, the state's largest university. Furthermore, the city of Boulder frequently acquires top rankings in health, well-being, quality of life, education, and art.