Direct answer
Area code 312 serves downtown Chicago only in Illinois. It is in the Central Time, and ten-digit dialing is required there.
Facts
| Area code | 312 |
| State | Illinois (IL) |
| Region | downtown Chicago only |
| Time zone | Central Time |
| Overlays | 312/773/872 |
| In service since | 1947 (NANPA tool date: 1 January 1947) |
| Dialing rule | Yes — ten-digit dialing is required in this overlay area. |
Areas covered
The 312 footprint covers the Loop, River North, Streeterville, the Magnificent Mile, the West Loop, the South Loop, the Near North Side, and the Near South Side. That list describes the area the code serves today, not the larger territory it may have covered when it was first assigned. Illinois is entirely in the Central Time Zone for this footprint. Callers in this area should always dial the full ten-digit number, including the area code, even for a local call.
History
Area code 312 is an original 1947 code, one of Illinois’s original codes alongside 217, 618, and 815, and it is not described here as a statewide code at launch. The suburbs split off as 708 in November 1989, leaving 312 with Chicago itself. Area code 773 then split from 312 in October 1996 for the rest of Chicago, leaving 312 as a downtown enclave surrounded by 773. Area code 872 was overlaid across both 312 and 773 in November 2009, so downtown Chicago numbers can now carry 312 or 872, and the wider city can also carry 773.
Dialing
Dialing rule: Yes — ten-digit dialing is required in this overlay area. The reason is the overlay structure in the facts table above, except where this page states a different reason, as it does for 616. From outside the United States, the country code for the United States is 1, followed by the area code and the local number. This page explains the area code only; it does not identify who owns a number or where a phone is.
Calls and spoofing
A call that shows a familiar area code is not proof of who is calling. Caller ID can be spoofed, so a number that looks local may come from anywhere. Do not share personal or financial details because of the number on the screen, and hang up and call back on a number you trust if a caller asks for money, codes, or account access. This site does not identify callers or phone owners, and it does not list reported spam numbers.
Related codes
773, 872 (overlay complex; 773 is not in 312’s own NANPA row but is corroborated by the split history).
Frequently asked questions
Where is 312 area code?
Area code 312 is in Illinois, covering downtown Chicago only. It does not cover the whole state.
What time zone is 312 area code?
Area code 312 is in the Central Time. Illinois is entirely in the Central Time Zone for this footprint.
What area codes overlay 312?
The overlay codes for 312 are 773; 872. The full overlay group is 312/773/872. New numbers in the same territory can carry any code in the group.
Is 312 area code a scam?
No area code is itself a scam. Scammers can spoof any area code, including this one, so judge a call by what the caller asks for, not by the number shown. This site does not identify callers.
When did 312 area code go into service?
Area code 312 has been in service since 1947 (NANPA tool date: 1 January 1947).
Sources
NANPA area code search; Area code 312
Based on a recent search of NANPA and official sources.
This website provides general information about North American area codes, compiled from public sources including NANPA. It is not affiliated with or endorsed by the FCC, NANPA or any telephone carrier. Area code details can change; confirm with your carrier or the official NANPA website. This site does not identify callers or phone owners.