| City | Area Code | Dialing Code |
|---|---|---|
| Arvada | 303 | +1 303 |
| Arvada | 720 | +1 720 |
| Aurora | 303 | +1 303 |
| Aurora | 720 | +1 720 |
| Boulder | 303 | +1 303 |
| Boulder | 720 | +1 720 |
| Brighton | 303 | +1 303 |
| Brighton | 720 | +1 720 |
| Broomfield | 303 | +1 303 |
| Broomfield | 720 | +1 720 |
| Castle Rock | 303 | +1 303 |
| Castle Rock | 720 | +1 720 |
| Castlewood | 303 | +1 303 |
| Castlewood | 720 | +1 720 |
| Colorado Springs | 719 | +1 719 |
| Columbine | 303 | +1 303 |
| Columbine | 720 | +1 720 |
| Commerce City | 303 | +1 303 |
| Commerce City | 720 | +1 720 |
| Denver | 303 | +1 303 |
| Denver | 720 | +1 720 |
| Englewood | 303 | +1 303 |
| Englewood | 720 | +1 720 |
| Fort Collins | 970 | +1 970 |
| Grand Junction | 970 | +1 970 |
| Greeley | 970 | +1 970 |
| Highlands Ranch | 303 | +1 303 |
| Highlands Ranch | 720 | +1 720 |
| Ken Caryl | 303 | +1 303 |
| Ken Caryl | 720 | +1 720 |
| Lafayette | 303 | +1 303 |
| Lafayette | 720 | +1 720 |
| Lakewood | 303 | +1 303 |
| Lakewood | 720 | +1 720 |
| Littleton | 303 | +1 303 |
| Littleton | 720 | +1 720 |
| Longmont | 303 | +1 303 |
| Longmont | 720 | +1 720 |
| Loveland | 303 | +1 303 |
| Loveland | 720 | +1 720 |
| Loveland | 970 | +1 970 |
| Northglenn | 303 | +1 303 |
| Northglenn | 720 | +1 720 |
| Parker | 303 | +1 303 |
| Parker | 720 | +1 720 |
| Pueblo West | 719 | +1 719 |
| Security-Widefield | 719 | +1 719 |
| Southglenn | 303 | +1 303 |
| Southglenn | 720 | +1 720 |
| Thornton | 303 | +1 303 |
| Thornton | 720 | +1 720 |
| Westminster | 303 | +1 303 |
| Westminster | 720 | +1 720 |
| Wheat Ridge | 303 | +1 303 |
| Wheat Ridge | 720 | +1 720 |