Castle Rock is a home-rule municipality that is the county seat of Douglas County, Colorado, United States. The most-populous municipality of the county, it had 48,231 resdents at the 2010 United States Census, with an estimated population of 64,484 as of 2019. It is named for the prominent, castle tower-shaped butte near the center of town. Midway between Denver and Colorado Springs, Castle Rock is part of the Denver metropolitan area and the Front Range Urban Corridor.
The region in and around Castle Rock was originally home to the Arapaho and Cheyenne peoples. They occupied the land between the Arkansas and South Platte Rivers.
White settlers were drawn to the area by rumors of gold and by land opened through the Homestead Act of 1862. However, the discovery of rhyolite stone, not gold, ultimately led to the settlement of Castle Rock.
Castle Rock was founded in 1874 when the eastern Douglas County border was redrawn to its present location. Castle Rock was chosen as the county seat because of its central location.