331 Area Code — Aurora, IL
Area code 331 serves Aurora and 3 other cities in Illinois. Local time follows America/Chicago. It overlays with 630, so 10-digit dialling is required.
- State
- Illinois
- Primary city
- Aurora
- Timezone
- America/Chicago
- In service since
- 2007
- Type
- Overlay
- Overlay codes
- 630
Overlay of 630
Cities Served by 331
The 331 area code covers 4 cities and communities in Illinois.
- Aurora
- Naperville
- Joliet
- Bolingbrook
About Area Code 331
Area code 331 is a North American Numbering Plan (NANP) area code that has been in service since 2007. It is administered by NANPA on behalf of the FCC and serves the Illinois region anchored on Aurora.
331 is an overlay code, which means it shares its geographic boundaries with one or more existing area codes (630). Overlays are created when a region exhausts the supply of phone numbers in its original area code. Within an overlay region, residents must dial all 10 digits even for local calls, because the same 7-digit number can exist under multiple area codes.
Mobile numbers in 331 are portable: a person who moved away from Aurora may still carry a 331 mobile number on their device. If you receive an unexpected call from a 331 number, run it through the reverse lookup tool above for the most accurate, free identification.
If you live or do business in Illinois, you may also interact with neighbouring or overlay codes (630). See the related codes section below to explore the rest of Illinois.
Other Illinois Area Codes
Continue exploring the Illinois numbering plan.
331 Area Code FAQ
Where is area code 331?
Area code 331 is located in Illinois, primarily serving Aurora and surrounding cities including Naperville, Joliet, Bolingbrook. The region operates on CT (America/Chicago) time.
What state is 331 area code?
331 is a Illinois area code. It was put into service in 2007 as an overlay and shares its geographic footprint with overlay code 630.
Is 331 a scam area code?
331 is a legitimate North American area code allocated by NANPA to Illinois. Like any geographic area code, scammers sometimes spoof 331 numbers — judge each call by content (urgent demands, unfamiliar transfers) rather than the area code alone. Run the specific number through our reverse lookup if you're unsure.
What time zone does 331 use?
Area code 331 operates on CT (America/Chicago). Numbers in this area code follow standard Illinois time-zone rules including any daylight-saving transitions for that region.
Can I look up a specific 331 phone number?
Yes. Use the reverse lookup widget above to enter a full 331 number. NumLocation returns the line type (mobile, landline, VoIP), carrier, rate-center city, and any public listings tied to the number — free.
What's the difference between 331 and 630?
331 and 630 cover the same Illinois geographic area as overlay codes. Calls between them are local, but you must dial all 10 digits. New phone numbers in this region are assigned from either pool depending on what's available with the carrier at signup.