Aurora, Colorado

Where Is Area Code 303?

Area code 303 serves north-central Colorado, including the Denver metropolitan area and nearby Front Range communities. It covers landline and mobile numbers in and around Denver, Aurora, Boulder, Lakewood, Westminster, and Thornton. Aurora is one of the major cities that uses 303, along with the overlapping area codes 720 and 983.

Area code 303 covers all or part of several counties in the Denver metro region. These include Denver County, Boulder County, Jefferson County, and Adams County, along with nearby communities tied to the same local calling region. The code reaches both urban centers and suburban cities along the eastern side of the Rocky Mountain Front Range.

This area includes well-known Colorado landmarks and institutions. Downtown Denver, the Colorado State Capitol, Red Rocks Park and Amphitheatre near Morrison, and the University of Colorado Boulder all sit within the broader 303 service area. The region lies just east of the Rocky Mountains and includes major transportation corridors such as Interstate 25 and Interstate 70.

History of Area Code 303

Area code 303 is one of the original North American area codes created in 1947. At first, it covered the entire state of Colorado. It remained the only area code in Colorado until 1988, when area code 719 was created for the southern and southeastern part of the state.

Area code 303 was reduced again in 1995, when area code 970 was assigned to northern and western Colorado. In 1998, area code 720 was added as an overlay for the same geographic area as 303 because the Denver metro region needed more phone numbers. Area code 983 began overlay service in the same region in 2022, adding a third code to the 303 and 720 service area.

Key Facts About Area Code 303

• Area code 303 is in Colorado and is strongly associated with Denver and Aurora.
• Area code 303 uses the Mountain Time Zone. It follows Mountain Standard Time and Mountain Daylight Time.
• Area code 303 is an original area code from 1947 under the North American Numbering Plan.
• Area code 303 now serves the same geographic region as area codes 720 and 983 through an overlay system.
• Area code 303 covers much of the Denver-Aurora-Lakewood metropolitan area in north-central Colorado.
• Major cities in the 303 area include Denver, Aurora, Boulder, Lakewood, Westminster, and Thornton.
• Notable institutions in the 303 region include the University of Colorado Boulder and major state government offices in Denver.
• Ten-digit dialing is required in the 303 region because 303 shares its service area with overlay area codes 720 and 983.

Frequently Asked Questions

What state is area code 303 in?

Area code 303 is in Colorado.

What major cities use area code 303?

Major cities that use area code 303 include Denver, Aurora, Boulder, Lakewood, Westminster, and Thornton.

Is area code 303 a toll-free number?

No. Area code 303 is a geographic area code for north-central Colorado.