331 Area CodeAurora, IL
Area code 331 covers Aurora and nearby communities in Illinois, in the Central Time (CT) zone, home to about 1.7 million people across 61 cities. It overlays 630, so the same region uses both and every local call needs all ten digits.
Overview
- Major City
- Aurora
- State
- Illinois (IL)
- Timezone
- Central Time (CT)
- Current Time
- Overlay
- Yes – shares area with 630
Where is area code 331?
Area code 331 serves part of Aurora, IL and the surrounding areas. It has a single overlay (630) that serves the same area.
Overview of the 331 Area Code
What is the 331 area code?
The 331 area code serves Aurora, Illinois, alongside other established area codes. When you see a 331 number, it indicates a local number within this geographic area.
Why was area code 331 created?
The 331 area code was introduced as an overlay to add numbers in Aurora once the existing area code 630 began to run out of available prefixes. It added a new supply of numbers without requiring current residents to change their existing digits.
Geographic Coverage of the 331 Area Code
The 331 area code serves Aurora and surrounding areas in Illinois. It operates within the Central Time (CT) time zone. It complements the coverage of area code 630. This area code covers several key cities, including:
- Aurora
- Naperville
- Joliet
- Bolingbrook
- Wheaton
- Downers Grove
Got a call from a 331 number? It came from Aurora, IL. Since 331 overlays with 630, every local call in the region needs all ten digits to land on the right line. Inside 331, Aurora holds about 11% of the population; the rest is split across 60 smaller cities.
Aurora Area Codes Overview
Aurora is served by multiple area codes, reflecting its telecommunications needs. The 331 area code operates alongside 630. Here are the area codes serving this region:
The introduction of the 331 area code helped prevent number exhaustion, ensuring a continuous supply of phone numbers across the geographic area.
What cities does area code 331 cover?
| City | State | Population | % of Area Code | % of City |
|---|---|---|---|---|
| Aurora | IL | 180,710 | 5% | 100% |
| Naperville | IL | 153,124 | 4% | 100% |
| Joliet | IL | 151,837 | 0% | 6% |
| Bolingbrook | IL | 74,756 | 2% | 91% |
| Wheaton | IL | 53,741 | 1% | 100% |
| Downers Grove | IL | 50,552 | 2% | 100% |
| Plainfield | IL | 48,881 | 1% | 20% |
| Elmhurst | IL | 46,108 | 1% | 100% |
| Lombard | IL | 44,490 | 1% | 100% |
| Romeoville | IL | 41,177 | 0% | 9% |
* Sources: Population – U.S. Census Bureau PEP, Vintage 2024 (SUB-IP-EST2024-POP). Area code assignments – NANPA CO Code data. See our data methodology.
Has area code 331 been reported for unwanted calls?
Yes – 181 unwanted-call complaints were reported to the FTC for numbers showing a 331 area code (May 29 – Jul 2, 2026).
- 45% robocalls
- ↑ 3% vs prior period
Most-reported subjects
- Other45%81
- Reducing your debt (credit cards, mortgage, student loans)14%26
- Dropped call or no message12%22
* Caller ID is easily spoofed, so these figures reflect the number shown on caller ID, not the caller's true location – an area code alone never identifies a caller. The FTC does not verify the facts in these complaints. Source: FTC Do Not Call (DNC) Reported Calls Data, retrieved 2026-07-05.
Which prefixes and exchanges belong to area code 331?
19% assigned to a telco
- 52% Landline
- 48% Wireless
- 0% Unknown
| Prefix | Usage | Carrier |
|---|---|---|
| (331)200- | Wireless | T-Mobile Usa |
| (331)201- | Wireless | Verizon Wireless |
| (331)202- | Wireless | Sprint Spectrum |
| (331)203- | Wireless | Sprint Spectrum |
| (331)204- | Landline | Onvoy |
| (331)205- | Wireless | T-Mobile Usa |
| (331)206- | Wireless | Sprint Spectrum |
| (331)207- | Landline | Level 3 Communications |
| (331)208- | Wireless | Sprint Spectrum |
| (331)209- | Landline | Level 3 Communications |
Frequently Asked Questions about the 331 Area Code
Who called me from a 331 number?
A 331 number is assigned to Aurora, Illinois, so a call may come from there. But caller ID is easy to fake, and scammers often spoof a local 331 code to look nearby, so a 331 number doesn't prove the caller is local. Recently, 181 unwanted-call complaints were reported to the FTC for numbers showing the 331 code (45% flagged as robocalls). If you don't recognize the number, let it go to voicemail; a real caller will leave a message.
Is 331 a scam area code?
No area code is a scam on its own. 331 is a normal, officially assigned code for Aurora, Illinois. Spam callers spoof local codes to raise the odds you answer, so 331 on your caller ID says nothing about who is really calling. Recently, 181 unwanted-call complaints were reported to the FTC for numbers showing the 331 code (45% flagged as robocalls). Judge the call itself, not the area code.
Why do I keep getting calls from the 331 area code?
Repeated calls from different 331 numbers are usually spoofing: a robocaller rotates through 331 numbers so each call looks local and slips past simple blocks. Recently, 181 unwanted-call complaints were reported to the FTC for numbers showing the 331 code (45% flagged as robocalls). Blocking one number rarely helps; voicemail screening, your carrier spam filter, and the Do Not Call Registry work better.
Should I answer an unknown 331 number?
If you aren't expecting a 331 call, let it ring to voicemail. Legitimate callers leave a message, most robocallers hang up when no one picks up, and answering can mark your number as active and bring more calls.
How do I block calls from the 331 area code?
Block a single 331 number from your recent-calls list (iPhone: tap the number, then Block this Caller; Android: tap the number, then Block or report spam). To cut the volume, turn on Silence Unknown Callers on iPhone or spam protection on Android, enable spam filtering from your carrier, and register at DoNotCall.gov. Blocking the entire 331 code also stops legitimate local calls, so use it only as a last resort.
Where is area code 331?
Area code 331 covers Aurora and the surrounding area in Illinois, spanning 61 cities with about 1,704,087 residents. It shares its area with overlay code 630.
Is 331 a real area code?
Yes. 331 is an active code in the North American Numbering Plan, assigned by NANPA and in service for Aurora, Illinois. A real code can still show up on spoofed spam calls, so treat unknown 331 calls with normal caution.
What timezone is the 331 area code in?
The 331 area code is in the Central Time (CT). Because a number can be kept when someone moves or switches to VoIP, a specific 331 caller may not be in that zone.
How do I call a 331 number from abroad?
From outside the US, dial your country's exit code, then 1 (the US country code), then 331 and the seven-digit number. From a mobile phone you can usually just enter +1 331 followed by the number and let the phone add the exit code for you.