Douglas County is the seventh-most populous of the 64 counties of the U.S. state of Colorado. As of the 2010 census, the population was 285,465. The county seat is Castle Rock. Douglas County is located midway between Colorado's two largest cities, Denver and Colorado Springs. It is lightly wooded, mostly with ponderosa pine, with broken terrain characterized by mesas, foothills and small streams. Cherry Creek and Plum Creek rise in Douglas County and flow north toward Denver and into the South Platte River. Douglas County was one of the original 17 counties created in the Colorado Territory by the Colorado Territorial Legislature on November 1, 1861.