The area code 720 is located in Boulder, Colorado.
Area code 720 serves Boulder, CO, as part of the Denver–Boulder metro along Colorado’s Front Range. It’s an overlay of 303, which means Boulder phone numbers can use either 720 or 303, and 10‑digit dialing is required for all local calls. The overlay was set up to handle rapid growth in phones and businesses, and it keeps Boulder connected to nearby cities across this busy corridor. In Boulder, you’ll see 720 on numbers tied to the University of Colorado Boulder, the Flatirons, and the lively Pearl Street Mall.
Area code 720 covers Boulder and many nearby communities, including:
Area code 720 was established in 1998 to expand numbering capacity while keeping existing 303 numbers in place, so no one had to change their number. The region now also uses area code 983 as an additional overlay alongside 303/720, reflecting steady growth in the Denver–Boulder area. Boulder’s mix of tech startups, research labs, and outdoor brands makes 720 a common sight on local business and campus contacts. For context, 303 is one of the original area codes from 1947, and 720 simply extends that same footprint across the metro.
720 overlay effective date: June 1, 1998 (North American Numbering Plan Administrator)