The City of Castle Pines is a home rule municipality located in Douglas County, Colorado, United States. The city population was 11,036 at the 2020 United States census. Castle Pines is a part of the Denver–Aurora–Lakewood, CO Metropolitan Statistical Area and the Front Range Urban Corridor. The city is located north of the Town of Castle Rock and south of the City of Lone Tree, Colorado.

The "City of Castle Pines North" was approved by popular vote on November 6, 2007, and officially incorporated with the first election of municipal officers on February 12, 2008. At the time of incorporation, Castle Pines was Douglas County's first new city since 1995, and Colorado's 271st municipality.

The "City of Castle Pines North" was officially renamed the "City of Castle Pines" by popular vote on November 2, 2010.

Castle Pines is located on Interstate 25 in central Colorado, 20 mi (32 km) south of downtown Denver and 43 mi (69 km) north of Colorado Springs.

The city lies in the Colorado Piedmont on the western edge of the Great Plains. Happy Canyon Creek runs north-northeast through the western part of the city, and Newlin Gulch and its tributary, South Newlin Gulch, run north-northeast and north, respectively, through the eastern part of the city. All three streams are part of the Cherry Creek watershed.

At the 2020 United States census, the city had a total area of 6,140 acres (24.849 km²), all of it land.

Lying within the Front Range Urban Corridor, the city is part of the greater Denver metropolitan area, and it borders two communities to its south: Castle Pines Village and Castle Rock, the county seat.

As of the 2020 census, Castle Pines had a population of 11,036. The median age was 44.4 years. 27.0% of residents were under the age of 18 and 15.1% of residents were 65 years of age or older. For every 100 females there were 97.5 males, and for every 100 females age 18 and over there were 94.3 males age 18 and over.