The state of Colorado, USA is currently served by a total of 4 area codes:
These Colorado area codes overlay (cover the same geographic area). The first code listed is the parent code. Overlay area codes are added when no more phone numbers are available in an existing Numbering Plan Area.
| City | County | Area code(s) |
|---|---|---|
| Arvada | Jefferson | 303/720 |
| Aurora | Adams | 303/720 |
| Boulder | Boulder | 303/720 |
| Brighton | Adams | 303/720 |
| Broomfield | Broomfield | 303/720 |
| Castle Rock | Douglas | 303/720 |
| Colorado Springs | El Paso | 719 |
| Commerce City | Adams | 303/720 |
| Denver | Adams | 303/720 |
| Englewood | Arapahoe | 303/720 |
| Fort Collins | Larimer | 970 |
| Fountain | El Paso | 719 |
| Grand Junction | Mesa | 970 |
| Greeley | Weld | 970 |
| Highlands Ranch | Douglas | 303/720 |
| Lafayette | Boulder | 303/720 |
| Lakewood | Jefferson | 303/720 |
| Littleton | Arapahoe | 303/720 |
| Longmont | Boulder | 303/720 |
| Loveland | Larimer | 970 |
| Parker | Douglas | 303/720 |
| Pueblo | Pueblo | 719 |
| Thornton | Adams | 303/720 |
| Westminster | Adams | 303/720 |
| Wheat Ridge | Jefferson | 303/720 |
| Windsor | Weld | 970 |