The 331 area code covers the same area as 630, including Roselle, Hinsdale and 31 more places in Illinois.
Area code 331 is in Illinois, on Central Time. In the 331 area, phone numbers are given out most in DuPage County, then Cook and Kane counties. It has been in service since October 7, 2007. 630 covers the same area, so two neighbours can have different area codes.
- Where
- 4 counties in Illinois, mostly DuPage County, Cook County and Kane County
- Time zone
- Central Time
- In service since
- October 7, 2007
- Shares its area with
- 630 (since 1996)
- Prefixes in use
- 224
- How to dial
- Local calls need 1, then the area code, then the number: 1-331-555-0142.
Find out who called you from a 331 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 (331) number is on today, use our free carrier lookup.
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Aurora holds 20% of the phone prefixes in area code 331.
A prefix is the three digits after the area code, and NANPA assigns each one to a town. Counting the 224 prefixes in use shows where 331 numbers are actually given out.
- Aurora45 prefixes, 20%
- Naperville33 prefixes, 15%
- Downers Grove21 prefixes, 9%
- Saint Charles18 prefixes, 8%
- Lombard13 prefixes, 6%
- Elmhurst10 prefixes, 4%
- Lemont10 prefixes, 4%
- Bartlett8 prefixes, 4%
Also served: Northbrook, Wheaton, Bensenville and Lemont and 21 smaller places.
Of the carriers named here, T-Mobile holds the most phone number prefixes in area code 331: 42 of 224.
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 224 prefixes in use in 331 divide between carriers; holders this page does not name are grouped as other carriers.
| Carrier | Prefixes | Share |
|---|---|---|
| T-MobileMobile network | 42 | 19% |
| AT&T MobilityMobile network | 26 | 12% |
| Fractel | 18 | 8% |
| BandwidthSupplies numbers to VoIP and app-based phone services | 11 | 5% |
| Ton80 Communications | 9 | 4% |
| Level 3 (Lumen)Lumen's business and wholesale network | 6 | 3% |
| 18 other carriers | 112 | 50% |
100% 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.
331 started in 2007 as an overlay on 630, and its ground has not changed since.
2007
331 starts on October 7, 2007, as an overlay on 630: new numbers on the same ground.
A 331 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 331 are 847, 312 and 708.
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 331.
Where is area code 331?
331 covers Roselle, Hinsdale, Naperville and La Grange and 29 more places in Illinois. In the 331 area, phone numbers are given out most in DuPage County, then Cook and Kane counties.
What state is area code 331 in?
Illinois. 331 is an Illinois area code on Central Time.
What cities use area code 331?
The places holding the most 331 prefixes are Roselle, Hinsdale, Naperville, La Grange, Downers Grove, Aurora, Elmhurst and Lombard, out of 33 places in all. The count comes from NANPA's prefix assignments as of October 1, 2026.
Which phone company owns area code 331?
No single phone company owns 331. NANPA's records list its 224 prefixes across many carriers, and the ones named on this page include T-Mobile, AT&T Mobility and Fractel. Numbers move between carriers, so check one exact number with a carrier lookup.
What time zone is area code 331 in?
331 is on Central Time.
When did area code 331 start?
331 went into service on October 7, 2007, as an overlay on 630: new numbers for the same area.
Is 331 the same area as 630?
Yes. 630 (since 1996) covers the same ground as 331. 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 331 number?
Local calls need 1, then the area code, then the number: 1-331-555-0142.
Is 331 a toll-free number?
No. 331 is a regular area code for Roselle and Hinsdale 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 331?
The closest are 847/224 (Northbrook, Illinois), 312/773/872 (Chicago, Illinois), 708/464 (La Grange, Illinois) and 815/779 (Rockford, Illinois), measured between the centres of each area.
Who called me from a 331 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 331 a scam?
331 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.