🇺🇸 331 area code
Area code 331 covers Aurora, Naperville, Elmhurst and Bensenville and the surrounding area in Illinois. It shares that territory with 630, so the same neighbourhood can have numbers in any of them. Enter a 331 number below for a free check before you call back.
- Location: Aurora, Illinois
- Time zone: Central (UTC−6)
- In service since October 7, 2007
Look up a number
Validity, carrier, line type, and region on the first pass.
Area code 331 at a glance
- Area code
- 331
- Location
- Illinois, United States
- Main cities
- Aurora, Naperville, Elmhurst, Bensenville, Oak Brook, Bolingbrook
- Time zone
- Central (UTC−6)
- Local time now
- —
- In service since
- October 7, 2007
- Created from
- 630
- Overlay codes
- 630
- Local calls
- Dial 1 + 10 digits
- Number format
- (331) 555-0123
- From abroad
- +1 331 555 0123
Cities in the 331 overlay area
- Aurora
- Naperville
- Elmhurst
- Bensenville
- Oak Brook
- Bolingbrook
- Wheaton
- St. Charles
- Downers Grove
- Lombard
Is a 331 call a scam?
An area code tells you where a number was first assigned, not where the caller is. Mobile numbers keep their area code when people move, and internet (VoIP) numbers can be picked in any area code — so a 331 number can be calling from anywhere.
Robocallers exploit that with "neighbor spoofing": showing a 331 number to people in Illinois because a local-looking call is more likely to be answered. If a 331 call claims to be your bank, the IRS or a delivery company, hang up and call the official number yourself.
About area code 331
331 entered service on October 7, 2007, as an overlay on 630, which had run short of numbers.
It is part of the 331/630 overlay: the codes cover the same area, and a new line there can be given a number in any of them. Two neighbours — or two phones in one household — can have different area codes. That is also why local calls need the full ten digits.
Because 331 overlays the same ground, the cities listed are those of the codes it shares with.
FAQ
Area code 331 questions
Sources: NANPA NPA database (11/04/2026) and Google libphonenumber. Area codes show where a number was assigned, not where its owner is today.
Where is area code 331?
Area code 331 is in Illinois, United States. It covers Aurora, Naperville, Elmhurst, Bensenville, Oak Brook and Bolingbrook.
What time zone is area code 331?
331 is in the Central (UTC−6) time zone, and observes daylight saving time.
What area codes overlay 331?
630 serves the same area as 331. Numbers in all of them are local to one another.
When did area code 331 start?
331 entered service on October 7, 2007, created from 630.
How do I find out who called me from 331?
Enter the full number in the lookup at the top of this page. The free check confirms whether the number is valid and shows its carrier, line type and region; a full report adds owner and public-web records where they are available.
Why am I getting calls from area code 331?
If you live in or near Illinois, they may be genuinely local — or robocalls spoofing a local-looking number. Unknown 331 callers who will not leave a message are best looked up before you call back.
Got a call from 331?
Run the free check first — validity, carrier, line type and region — and unlock the full report only if you need it.