The 312 area code covers Chicago, Wheeling and 4 more places in Illinois.
Area code 312 is in Illinois, on Central Time. In the 312 area, phone numbers are given out most in Cook County, then DuPage County. It has been in service since 1947. 872 covers the same area, so two neighbours can have different area codes.
- Where
- Cook County and DuPage County, Illinois
- Time zone
- Central Time
- In service since
- 1947, one of the original area codes
- Shares its area with
- 872 (since 2009)
- Prefixes in use
- 784
- How to dial
- Local calls need 1, then the area code, then the number: 1-312-555-0142.
Find out who called you from a 312 number.
Enter the full 10-digit number to see who it is listed to and the city and state on the listing. It is the same free check as our who called me lookup. To see only the caller ID name on the number, use our free CNAM lookup. To see whether it is a mobile, a landline or a VoIP line, use our free VoIP checker. To see which carrier a (312) number is on today, use our free carrier lookup.
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Chicago holds 95% of the phone prefixes in area code 312.
A prefix is the three digits after the area code, and NANPA assigns each one to a town. Counting the 784 prefixes in use shows where 312 numbers are actually given out.
- Chicago748 prefixes, 95%
- Wheeling12 prefixes, 2%
- Hinsdale11 prefixes, 1%
- La Grange8 prefixes, 1%
- Northbrook3 prefixes, <1%
- Roselle2 prefixes, <1%
Illinois Bell (AT&T) holds the most phone number prefixes in area code 312: 334 of 784.
NANPA, which runs the North American numbering plan, assigns each prefix (the three digits after the area code) to one carrier. Here is how the 784 prefixes in use in 312 divide between carriers; holders this page does not name are grouped as other carriers.
| Carrier | Prefixes | Share |
|---|---|---|
| Illinois Bell (AT&T)AT&T's landline company | 334 | 43% |
| AT&T MobilityMobile network | 82 | 10% |
| T-MobileMobile network | 64 | 8% |
| Level 3 (Lumen)Lumen's business and wholesale network | 34 | 4% |
| SpokPaging network | 33 | 4% |
| Teleport (AT&T)AT&T's business phone network | 22 | 3% |
| 26 other carriers | 215 | 27% |
53% of these prefixes are pooled, which means the blocks of 1,000 numbers inside them can belong to other carriers. Any number can also have been moved to another carrier since, so this shows who holds the prefixes, not who serves a given number.
Want the carrier of one exact number? Our free carrier lookup checks it, because numbers move between carriers.
Source: NANPA central office code assignments, October 1, 2026.
312 has been split 2 times and overlaid once since 1947.
1947
312 is one of the original North American area codes.
1989
On November 11, 1989, 708 splits off and takes part of the 312 area.
1996
On October 12, 1996, 773 splits off and takes part of the 312 area.
2009
On November 7, 2009, 872 is added on top of 312, so new numbers here can get either code.
A 312 number on your screen can still be a scam, because caller ID is easy to fake.
- Let an unknown call go to voicemail. A real caller leaves a message; a robocaller usually does not.
- Look the number up with the box above before you call back, because calling back tells a robocaller your line is live.
- Hang up on anyone who wants gift cards, crypto or a wire transfer, or asks you to read out a code that was just texted to you.
- Report unwanted robocalls at reportfraud.ftc.gov, or paste a suspicious message into our free scam checker.
The area codes closest to 312 are 708, 630 and 847.
This list measures the distance between the centres of each area, across state lines, and shows codes that share one area together.
These are the questions people ask most about area code 312.
Where is area code 312?
312 covers Chicago, Wheeling, Hinsdale and La Grange and 2 more places in Illinois. In the 312 area, phone numbers are given out most in Cook County, then DuPage County.
What state is area code 312 in?
Illinois. 312 is an Illinois area code on Central Time.
What cities use area code 312?
The places holding the most 312 prefixes are Chicago, Wheeling, Hinsdale, La Grange, Northbrook and Roselle. The count comes from NANPA's prefix assignments as of October 1, 2026.
Which phone company owns area code 312?
No single phone company owns 312. NANPA's records show Illinois Bell (AT&T) holds the most 312 prefixes, 334 of 784, followed by AT&T Mobility and T-Mobile. Numbers move between carriers, so check one exact number with a carrier lookup.
What time zone is area code 312 in?
312 is on Central Time.
When did area code 312 start?
312 is one of the original North American area codes, in service since 1947.
Is 312 the same area as 872?
Yes. 872 (since 2009) covers the same ground as 312. Nobody's number changed when it was added; new lines simply get whichever code has numbers left, so two neighbours can have different codes.
How do I dial a 312 number?
Local calls need 1, then the area code, then the number: 1-312-555-0142.
Is 312 a toll-free number?
No. 312 is a regular area code for Chicago and Wheeling in Illinois, not a toll-free one. The toll-free codes in North America are 800, 833, 844, 855, 866, 877 and 888.
What area codes are near 312?
The closest are 708/464 (La Grange, Illinois), 630/331 (Roselle, Illinois), 847/224 (Northbrook, Illinois) and 815/779 (Rockford, Illinois), measured between the centres of each area.
Who called me from a 312 number?
Enter the full 10-digit number in the lookup above. It returns the listed owner where there is a public record, where the number is registered, and whether it is a mobile, a landline or a VoIP line.
Is area code 312 a scam?
312 is a real Illinois area code, so the code itself is not a warning sign. Scam callers fake local-looking numbers on purpose, so judge the call by what the caller asks for, and look the number up before calling back.
Put this lookup on your site: our free area code widget takes two lines of code and shows any US area code's state, time zone and local time.
Source: NANPA, the North American Numbering Plan Administrator: its area code database and prefix assignments, as of October 1, 2026.