Significant events for area code 303
| Date |
Details |
| 1947 | The original area code for Colorado |
| March 5, 1988 | Area code 303 was split with 719 covering southeasten Colorado. |
| April 2, 1995 | Area code 303 was split with 970 covering northern and western Colorado. |
| September 1, 1998 | Area code 720 was overlaid on 303. |
| June 17, 2022 | Area code 983 was overlaid on 303. |