The 303 area code is the original Colorado area code, now mostly associated with Denver, Boulder, and the surrounding Front Range suburbs in the Mountain time zone.

What is the 303 area code?

  • It is a North American Numbering Plan (NANP) telephone area code for north‑central Colorado.
  • It primarily serves Denver, Boulder, Aurora, Lakewood, Thornton, Longmont, and nearby suburbs along the Front Range.
  • It sits in the Mountain time zone (GMT −07:00, with daylight saving in most of the region).

Quick facts (mini “Quick Scoop”)

  • State: Colorado.
  • Major cities: Denver, Aurora, Boulder, Lakewood, Thornton, Longmont, Castle Rock.
  • Major counties: Denver, Jefferson, Arapahoe, Adams, Weld, plus others (10 counties total).
  • Population covered: Around 3.9 million people when combined with its overlays.
  • Time zone: Mountain.
  • Overlays: 720 (since 1998) and 983 (since 2022); all three codes cover the same geographic region.
  • Dialing: Ten‑digit dialing is required within this area because of the overlay setup.
  • History: 303 was created in 1947 as one of the original U.S. area codes and originally covered the entire state of Colorado before being reduced to the Denver/Front Range region.

HTML table: core 303 details

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Item Details
Area code 303 telephone area code in the North American Numbering Plan (NANP).
State Colorado (north‑central portion of the state).
Primary metro area Denver metropolitan area and nearby Front Range cities.
Major cities Denver, Aurora, Boulder, Lakewood, Thornton, Longmont, Castle Rock and surrounding suburbs.
Counties covered 10 counties including Denver County, Jefferson County, Arapahoe County, Adams County, Weld County.
Time zone Mountain Time (GMT −07:00, with daylight saving observed in most areas).
Overlays Overlayed by area codes 720 (since 1998) and 983 (since 2022).
Dialing pattern Ten‑digit dialing required within the 303/720/983 complex.
Population served Combined 303 + overlays serve roughly 3.9 million people in the region.
Year created Established in 1947 as one of the original U.S. area codes.

History and “identity” of 303

  • 303 started as the single area code for all of Colorado, then shrank geographically as new codes were introduced and population grew.
  • The growth of Denver, Boulder, and the tech and energy sectors along the Front Range led to number exhaustion, prompting the 720 overlay in 1998 and the newer 983 overlay in 2022.
  • In recent years, 303 has taken on a kind of local “badge of honor” in Denver/Boulder, often seen as the classic or original Mile High City code compared with newer overlays.

You might see it referenced in local branding, business numbers, and even social media handles to signal a long‑time local presence.

Scam and safety notes (2024–2026 context)

Because 303 is widely recognized and trusted around Denver and Boulder, scammers sometimes spoof 303 numbers to make their calls look local and credible.

Recent warnings and patterns:

  • Law‑enforcement impostor scams: The Denver Sheriff Department has warned about fake “jury duty warrant” calls from spoofed 303 numbers demanding payment via cryptocurrency like Bitcoin.
  • Neighbor spoofing: Robocallers display 303 numbers that look similar to yours (same area code and prefix) so you are more likely to pick up.

Basic safety tips if you get an unexpected 303 call:

  • Do not share personal or financial information with unsolicited callers, even if the number looks local.
  • If the caller claims to be a government office, bank, or utility, hang up and call the official published number instead.
  • Be skeptical of threats, urgency, or demands for payment via gift cards, wire transfers, or crypto.

These patterns are similar to scams in many U.S. area codes; 303 is not “more dangerous” by definition, but its local trust factor makes it attractive to scammers.

Information gathered from public forums or data available on the internet and portrayed here.