Illinois · Central Time
312 Area Code
Area code 312 is in Illinois, serving downtown Chicago, including the Loop and nearby central neighborhoods. It is in the Central Time zone. It shares its territory with overlay code 872, so 10-digit dialing is required.
Last updated October 1, 2026 · Source: NANPA
Where is the 312 area code?
312 is a Illinois area code covering downtown Chicago, including the Loop and nearby central neighborhoods. In the wider directory it sits in the Midwest region.
Cities in the 312 area code
Counties served by 312
Cook County.
312 overlay codes and dialing
The 312 territory is covered by an overlay of 2 area codes: 312, 872. All of them serve the same geographic area, and the original code is 312. Because more than one code covers the same ground, 10-digit dialing is mandatory — you must dial the area code for every local call. New phone lines may be assigned any of these codes.
History of the 312 area code
312 is one of the original area codes assigned in 1947, when AT&T and Bell Laboratories created the North American Numbering Plan and divided the country into the first 86 numbering plan areas. It has served the Chicago area ever since, with 872 later added as an overlay to supply more numbers.
Is 312 a scam or spam risk?
312 is a legitimate geographic area code, not a premium or toll line, so a call from it costs you nothing extra. That said, scammers frequently spoof real local area codes to look familiar on caller ID. A genuine 312 number on your screen is no guarantee the caller is in Chicago, IL or trustworthy. See spam & scam-risk area codes for how spoofing works and how to respond.
Other Illinois area codes
Explore more
See every code in Illinois, compare codes across the Midwest region, or view all Central Time codes. You can also browse the 3XX block or the complete numeric list of US area codes.
New to how this all works? Start with how area codes work, then read up on overlays, 10-digit dialing, and spam & scam-risk codes. To check another number, use the area code lookup tool.
Quick answers
312 area code FAQ
Where is the 312 area code?
The 312 area code is in Illinois, covering downtown Chicago, including the Loop and nearby central neighborhoods, in the Midwest region.
What cities are in the 312 area code?
Cities in the 312 area code include Chicago.
What time zone is 312 in?
312 is in the Central Time zone.
What is the overlay for the 312 area code?
312 shares its territory with 872. Both codes (312, 872) serve the same area, so 10-digit dialing is required for every call.
When did the 312 area code start?
312 went into service on January 1, 1947 as one of the original 1947 North American area codes.
Do I have to dial 10 digits for 312?
Yes. Because 312 is an overlay area, you must dial the full 10-digit number (area code + 7 digits) for every call.
Is 312 a toll-free or premium code?
No. 312 is a standard geographic area code, so calling it costs the same as any local or long-distance call on your plan. Toll-free calls use 800, 888, 877, 866, 855, 844 or 833.