312 area code
Where the 312 area code is, its overlay and how to dial a +1 312 number from anywhere.
The 312 area code is in Chicago, Illinois, United States (Central (CT)). To call from abroad: +1 312 555-0123. It is an overlay, so all 10 digits are dialled.
The 312 area code is a geographic North American Numbering Plan (NANP) code covering Chicago, Illinois. It has been in service since 01-Jan-1947 and sits in the Central (CT) time zone.
How to dial a 312 number
+1 312 555-01231 312 555-0123312 555-0123Cities in the 312 area code
A 312 number is usually in one of these places in Illinois — 1 county.
Other Illinois area codes
Frequently asked questions
Where is the 312 area code?
The 312 area code is in Chicago, Illinois, United States (Central (CT)).
Is 312 an overlay area code?
Yes. 312 overlays the same region as 872, so callers dial all 10 digits.
Do I have to dial 10 digits for 312?
Yes — dial the area code plus the seven-digit number.
How do I call a 312 number from another country?
Dial your exit code (or +), then 1, then 312, then the number: +1 312 555-0123.
Source: NANPA numbering plan. An area code covers a region, not a precise address — a 312 number does not pinpoint a street or ZIP code.
Number holders in area code 312
Each prefix (the three digits after the area code) is assigned by NANPA to one telephone company. 798 prefixes are in use in 312, shared by 39 companies. The largest holders:
| Company | Prefixes | Share |
|---|---|---|
| Illinois Bell Tel Co | 334 | 42% |
| New Cingular Wireless PCS, LLC | 82 | 10% |
| T-Mobile USA, Inc. | 64 | 8% |
| Cellco Partnership Dba Verizon Wireless | 54 | 7% |
| Mcimetro Access Transmission Services LLC | 33 | 4% |
| Spok, Inc. | 33 | 4% |
Source: NANPA central office code assignments. A number keeps its original prefix when it is ported to another carrier.
Complaints about 312 numbers
- Reports to the FTC, last 30 days
- 385
- Recorded messages or robocalls
- 46%
- Rank among area codes
- #253 of 670
- Most reported subjects
- Other (184)
- Dropped call or no message (65)
- Reducing your debt (credit cards, mortgage, student loans) (36)
Period Aug 26 – Sep 24, 2026. These are the numbers shown on the caller ID of the reported calls; many are spoofed and do not belong to the real caller.
Source: US Federal Trade Commission, Do Not Call reported calls data (daily files).
All US area codes United States +1 Map of area code 312 — cities & rate centres