Thornton, Colorado
Mountain Time Zone (UTC-7) · CO · —
303
⬡ 1947
Denver
Colorado
Mountain
+2
720
2001
Denver
Colorado
Mountain
Overlay
983
2024
Denver
Colorado
Mountain
Overlay
About Area Codes in Thornton, Colorado
Thornton, Colorado is served by 3 area codes: 303, 720, 983. When multiple area codes serve the same geographic area, it typically indicates overlay codes have been added to accommodate growing demand for phone numbers. All local calls within Thornton require 10-digit dialing. The city is in the Mountain time zone (UTC-7).
Other cities in area code 303
Frequently Asked Questions
What area code is Thornton, Colorado?
Thornton, Colorado uses area codes 303 and 720 and 983.
What time zone is Thornton in?
Thornton is in the Mountain time zone (UTC-7).
Do I need to dial 10 digits when calling Thornton?
Yes, all local calls in Thornton require 10-digit dialing because the area is served by multiple overlay area codes.
When was area code 303 created?
Area code 303 is one of the original 86 area codes established in 1947 as part of the North American Numbering Plan (NANP).
What cities share area code 303 with Thornton?
Other cities sharing area code 303 with Thornton include Arvada, Aurora, Boulder, Brighton, Broomfield, among others.
Thornton, CO · Mountain Time Zone