303
Covers Colorado
Overlay with 720 and 983
City facts
Castle Rock area codes
Area codes for Colorado: history, overlays and how to dial.
303720983
Castle Rock uses area codes 303, 720 and 983. Because more than one area code serves the same area, local calls need all ten digits.
About these area codes
720
Covers Colorado
In service since 1998
Overlay with 303 and 983
983
Covers Colorado
In service since 1998
Overlay with 303 and 720
How to call a number in Castle Rock
Inside the US
1 (303) 555-0123Dial 1, the area code, then the seven-digit number.Local call
(303) 555-0123Overlay area: always include the area code.From outside the US
+1 303 555 0123Use your country's exit code or +, then 1 for the US.Castle Rock is on Mountain Time (MT); check the time before calling from another zone.
Other cities that share these codes
Castle Rock quick facts
Castle Rock was founded in 1874 and incorporated on April 14, 1881.
Founded1874
Incorporated1881April 14, 1881
CountyDouglas CountyColorado
Area codes303, 720, 983Population76,614Census ACS estimateZIP codes380104, 80108, 80109Elevation6,224 ft1,897 m
Time zoneMountain TimeMT
Dates, namesake and elevation from Wikipedia: Castle Rock, Colorado and Wikidata (checked 2026-11-08); population and ZIP codes from the U.S. Census Bureau.
Questions
What area code is Castle Rock?
Castle Rock uses area codes 303, 720 and 983. Because more than one area code serves the same area, local calls need all ten digits.
When did area code 720 start?
Area code 720 dates from 1998.
When did area code 983 start?
Area code 983 dates from 1998.
Do I need to dial the area code for local calls in Castle Rock?
Yes. 303, 720 and 983 share the same area as an overlay, so every local call needs the area code plus the seven-digit number (ten digits).
What time zone is area code 303 in?
Castle Rock is on Mountain Time (MT).
What other cities use area code 303?
Other cities in this network that share 303, 720 and 983 include Breckenridge.
Sources: Area codes 303, 720, and 983, Area codes 303, 720, and 983, Area codes 303, 720, and 983 (Wikipedia) and Wikidata, checked 2026-11-08. Numbering plans change; the North American Numbering Plan Administrator is the official record.