Geographic Regions and Area Codes in Area Code 303

Area Code 303 covers a significant portion of central Colorado, including major cities such as Denver, Boulder, and Aurora. This area code also encompasses surrounding suburbs like Lakewood, Littleton, Longmont, Broomfield, and Castle Rock. The region is divided into 10 counties: Adams, Arapahoe, Boulder, Broomfield, Clear Creek, Denver, Douglas, Gilpin, Jefferson, and Weld. To accommodate the growing demand for telephone numbers, Area Code 303 is overlaid by area codes 720 and 983.

The 983 overlay was activated on June 17, 2022, following Colorado Public Utilities Commission approval to address projected number exhaustion. This addition maintains the same geographic coverage while providing additional numbering resources for the region's continued growth.

Key cities and their area codes include:

  • Denver: 303, 720, 983
  • Boulder: 303, 720, 983
  • Aurora: 303, 720, 983
  • Lakewood: 303, 720, 983
  • Littleton: 303, 720, 983
  • Longmont: 303, 720, 983
  • Broomfield: 303, 720, 983
  • Castle Rock: 303, 720, 983