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Longmont Safety and Justice Center. The City of Longmont is a Home Rule Municipality in Boulder and Weld counties of the U.S. state of Colorado. Longmont is located northeast of the county seat of Boulder and 33 miles (53 km) north-northwest of the Colorado State Capitol in Denver. Longmont's population was 86,270 at the time of the 2010 U.S. Census. Longmont is the 13th most populous city in the state of Colorado.
Longmont by the Numbers. Longmont, Colorado, located within Boulder County, is a city with 22 square miles, more than 300 days of sunshine and a spectacular vista of the Rocky Mountains. Longmont sits at an elevation of 4,979 feet above sea level. With more than 1,500 acres of parks and open space, Longmont is perfect for outdoor enthusiasts.