The Town of Castle Rock is a home rule municipality that is the county seat of Douglas County, Colorado, United States. Castle Rock is located about 35 miles south of Denver and 40 miles north of Colorado Springs on the Interstate 25 corridor just east of the front range of the Rocky Mountains. The town is the center of the burgeoning urbanization of the county. Castle Rock is named after a small prominent butte just north of the town, clearly visible from Interstate 25. Public access is provided to climb to the top of the rock. Castle Rock is on East Plum Creek, a small stream which periodically floods. As of 2005, the city is estimated to have a total population of 35,745. Castle Rock is now the 19th most populous municipality in the State of Colorado. Castle Rock apartments for rent comparison page shows most up to date rent information on Castle Rock apartments and houses. Rent information is obtained from multiple rental sources but we cannot guarantee their accuracy.