Boulder County administrative offices are located at 2025 14th Street, Boulder, CO 80302; phone: 303‑441‑3525.
Boulder County is located northwest of Denver in the north-central part of Colorado. The county sits on the eastern slope of the Rocky Mountains, with the Continental Divide serving as its western border. The western three-fifths of the county is mountainous, while the eastern portion is rolling plains. Elevations within the boundaries of the county range from 14,000 foot peaks in the Rocky Mountains to about 5,000 feet on the plains. The county encompasses 741 square miles and contains diversified settings, both rural and urban. The county population was approximately 214,978 in 2005; about 86,969 of those reside in Boulder, 56,065 in Longmont, 15,995 in Lafayette, 14,356 in Louisville and the remainder in the smaller towns of Lyons, Nederland, Ward, Jamestown, Superior, and Erie and unincorporated areas, which include the communities of Niwot, Gunbarrel and Allenspark. Native Americans were the first to inhabit the area; the Utes were long-time residents of the "Shining Mountains," followed later by the Cheyenne and Arapaho Indians who hunted in the Boulder and St. Vrain valleys prior to the arrival of the first Euro-American settlers. The discovery of gold led to the first town, Boulder City, being laid out in March 1859. The Colorado Territory was created in 1861, and Boulder was one of the first seventeen counties.