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331 Area CodeAurora, IL

Area code 331 covers Aurora and nearby communities in Illinois, in the Central Time (CT) zone, home to about 1,703,350 people across 61 cities. It was added in 2007 as an overlay of 630, so the same region uses both codes 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

Nearby Area Codes

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?

Area code 331 went into service on October 7, 2007, as an overlay of 630. An overlay adds a second code to the same territory instead of splitting it: existing 630 numbers kept their digits, new lines began receiving 331 numbers, and local calls in the region require all ten 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. Of the listed cities' population, Aurora accounts for about 10.6%; 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:

331630

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?

CityStatePopulationPopulation in 331% of listed-city population% of City
AuroraIL180,710180,71010.6%100.0%
NapervilleIL153,124148,9189.0%97.3%
JolietIL151,83708.9%0.0%
BolingbrookIL74,75668,2884.4%91.3%
WheatonIL53,74153,7413.2%100.0%
Downers GroveIL50,55250,5523.0%100.0%
PlainfieldIL48,8816,9852.9%14.3%
ElmhurstIL46,10846,1082.7%100.0%
LombardIL44,49044,4902.6%100.0%
RomeovilleIL41,1774,6102.4%11.2%
BartlettIL40,71836,4522.4%89.5%
Carol StreamIL39,55639,5562.3%100.0%
OswegoIL38,77838,7782.3%100.0%
StreamwoodIL38,36034,9352.3%91.1%
Hanover ParkIL36,68536,6852.2%100.0%
AddisonIL35,72835,7282.1%100.0%
WoodridgeIL34,10334,1032.0%100.0%
St. CharlesIL33,48233,4822.0%100.0%
Glendale HeightsIL32,86632,8661.9%100.0%
Glen EllynIL28,87228,8721.7%100.0%
BataviaIL26,55526,5551.6%100.0%
YorkvilleIL25,98625,9861.5%100.0%
West ChicagoIL25,46925,4691.5%100.0%
WestmontIL24,30824,3081.4%100.0%
LisleIL23,54823,5481.4%100.0%
RoselleIL22,87122,8711.3%100.0%
BloomingdaleIL22,62222,6221.3%100.0%
Villa ParkIL22,02022,0201.3%100.0%
DarienIL22,01522,0151.3%100.0%
MontgomeryIL21,95721,9571.3%100.0%
GenevaIL21,16821,1681.2%100.0%
North AuroraIL19,32919,3291.1%100.0%
BensenvilleIL18,62918,6291.1%100.0%
LemontIL18,20318,2031.1%100.0%
HinsdaleIL17,59817,5981.0%100.0%
WarrenvilleIL15,24715,2470.9%100.0%
Wood DaleIL13,98313,9830.8%100.0%
PlanoIL12,67712,6770.7%100.0%
Burr RidgeIL11,20211,2020.7%100.0%
Campton HillsIL10,89410,8940.6%100.0%
WinfieldIL10,19910,1990.6%100.0%
ItascaIL9,5069,5060.6%100.0%
Sugar GroveIL9,3399,3390.5%100.0%
WillowbrookIL9,1799,1790.5%100.0%
Clarendon HillsIL8,7038,7030.5%100.0%
Oak BrookIL8,1888,1880.5%100.0%
Boulder HillIL8,1088,1080.5%100.0%
SandwichIL7,29900.4%0.0%
ElburnIL6,8266,8260.4%100.0%
Willow SpringsIL5,79300.3%0.0%
Palos ParkIL4,8102,9080.3%60.5%
Indian Head ParkIL3,95600.2%0.0%
Oakbrook TerraceIL2,7292,7290.2%100.0%
WayneIL2,2852,2850.1%100.0%
PrestburyIL1,7221,7220.1%100.0%
Maple ParkIL1,48200.1%0.0%
Big RockIL1,0861,0860.1%100.0%
Lily LakeIL1,0591,0590.1%100.0%
KanevilleIL4474470.0%100.0%
VirgilIL2842840.0%100.0%
MillbrookIL28200.0%0.0%

City population is shown in full. The share of each city inside 331 is measured from Census tract centroids, not estimated from a rate-center match – so a city split between two codes appears on both, at the fraction each one actually holds. The “% of listed-city population” column uses the full populations of the cities listed here.

What counties does area code 331 cover?

1,703,350 residents across 5 counties, counted inside the 331 boundary — a county split between codes contributes only its part.

CountyStatePopulation in 331% of area-code footprint% of County
DuPage CountyIL932,87755%100%
Kane CountyIL293,03417%57%
Cook CountyIL224,23113%4%
Will CountyIL141,2788%20%
Kendall CountyIL111,9307%85%

Sources: City populations – U.S. Census Bureau PEP, Vintage 2024 (SUB-IP-EST2024-POP). State populations – the same program, Vintage 2025 (CO-EST2025-ALLDATA). Area-code footprint and county populations – 2020 Census Centers of Population, mapped against NANP area code boundaries. The share of each city inside a code is measured the same way, against Census place boundaries from the Census Bureau's TIGERweb service. Area code assignments – NANPA CO Code data. See our data methodology.

Has area code 331 been reported for unwanted calls?

Yes – 1,081 unwanted-call complaints were reported to the FTC for numbers showing a 331 area code (May 29 – Aug 14, 2026).

  • 74% robocalls
  • ↑ 325% vs prior period

Most-reported subjects

  • Reducing your debt (credit cards, mortgage, student loans)43%467
  • Other33%361
  • Calls pretending to be government, businesses, or family and friends9%93

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 2026-08-17.

Which prefixes and exchanges belong to area code 331?

19% assigned to a telco

  • 52% Landline
  • 48% Wireless
  • 0% Unknown
PrefixUsageCarrier
(331)200-WirelessT-Mobile Usa
(331)201-WirelessVerizon Wireless
(331)202-WirelessSprint Spectrum
(331)203-WirelessSprint Spectrum
(331)204-LandlineOnvoy
(331)205-WirelessT-Mobile Usa
(331)206-WirelessSprint Spectrum
(331)207-LandlineLevel 3 Communications
(331)208-WirelessSprint Spectrum
(331)209-LandlineLevel 3 Communications
(331)210-LandlinePeerless Network Of Illinois
(331)212-LandlineMcimetro Access Transmission Services
(331)213-WirelessVerizon Wireless
(331)214-WirelessVerizon Wireless
(331)215-WirelessVerizon Wireless
(331)216-WirelessNew Cingular Wireless Pcs
(331)218-WirelessT-Mobile Usa
(331)219-LandlineTelnyx
(331)220-WirelessSprint Spectrum
(331)221-LandlineIllinois Bell Tel Co
(331)222-WirelessNew Cingular Wireless Pcs
(331)223-WirelessNew Cingular Wireless Pcs
(331)225-WirelessSprint Spectrum
(331)226-WirelessT-Mobile Usa
(331)227-WirelessVerizon Wireless
(331)228-LandlineOvation Communications Of Illinois
(331)229-WirelessVerizon Wireless
(331)230-WirelessT-Mobile Usa
(331)231-WirelessNew Cingular Wireless Pcs
(331)232-WirelessNew Cingular Wireless Pcs
(331)233-LandlineTelnyx
(331)234-WirelessVerizon Wireless
(331)235-WirelessNew Cingular Wireless Pcs
(331)236-WirelessT-Mobile Usa
(331)237-LandlineMcimetro Access Transmission Services
(331)238-LandlineTeleport Communications America
(331)239-LandlineOnvoy
(331)240-LandlinePeerless Network Of Illinois
(331)241-LandlineOnvoy
(331)242-WirelessT-Mobile Usa
(331)243-WirelessT-Mobile Usa
(331)244-LandlineOnvoy
(331)245-WirelessT-Mobile Usa
(331)246-WirelessT-Mobile Usa
(331)247-LandlineVonage America
(331)248-LandlineComcast Ip Phone
(331)249-LandlineOnvoy
(331)250-WirelessT-Mobile Usa
(331)251-WirelessVerizon Wireless
(331)252-LandlineTeleport Communications America
(331)253-WirelessT-Mobile Usa
(331)254-WirelessT-Mobile Usa
(331)255-LandlineOnvoy
(331)256-WirelessVerizon Wireless
(331)257-WirelessNew Cingular Wireless Pcs
(331)258-LandlineOnvoy
(331)259-LandlinePeerless Network Of Illinois
(331)260-LandlineTeleport Communications America
(331)261-WirelessT-Mobile Usa
(331)262-WirelessSprint Spectrum
(331)263-LandlineOnvoy
(331)264-LandlineLevel 3 Communications
(331)265-LandlineOnvoy
(331)266-WirelessNew Cingular Wireless Pcs
(331)267-LandlineVonage America
(331)268-WirelessT-Mobile Usa
(331)269-WirelessT-Mobile Usa
(331)270-LandlineOnvoy
(331)271-LandlineOnvoy
(331)272-LandlineOnvoy
(331)273-LandlineOnvoy
(331)274-WirelessT-Mobile Usa
(331)275-WirelessT-Mobile Usa
(331)276-WirelessVerizon Wireless
(331)277-WirelessNew Cingular Wireless Pcs
(331)278-WirelessNew Cingular Wireless Pcs
(331)279-LandlinePaetec Communications
(331)280-WirelessVerizon Wireless
(331)281-LandlineIllinois Bell Tel Co
(331)282-LandlineOnvoy
(331)283-WirelessT-Mobile Usa
(331)284-WirelessT-Mobile Usa
(331)285-WirelessVerizon Wireless
(331)286-WirelessVerizon Wireless
(331)287-LandlineBandwidth.Com Clec
(331)288-LandlineTon80 Communications
(331)289-WirelessT-Mobile Usa
(331)290-WirelessVerizon Wireless
(331)291-WirelessVerizon Wireless
(331)292-LandlineOnvoy Spectrum
(331)293-WirelessNew Cingular Wireless Pcs
(331)294-WirelessVerizon Wireless
(331)295-LandlineNuso
(331)299-LandlineFractel
(331)300-WirelessT-Mobile Usa
(331)301-LandlineMetropcs
(331)302-WirelessVerizon Wireless
(331)303-LandlineBandwidth.Com Clec
(331)304-WirelessT-Mobile Usa
(331)305-WirelessVerizon Wireless
(331)307-WirelessT-Mobile Usa
(331)308-LandlineBandwidth.Com Clec
(331)310-LandlineBandwidth.Com Clec
(331)313-LandlineOnvoy Spectrum
(331)315-WirelessNew Cingular Wireless Pcs
(331)318-LandlineBandwidth.Com Clec
(331)321-WirelessT-Mobile Usa
(331)330-WirelessNew Cingular Wireless Pcs
(331)332-WirelessNew Cingular Wireless Pcs
(331)333-WirelessNew Cingular Wireless Pcs
(331)334-LandlineOnvoy
(331)336-LandlineFractel
(331)341-LandlineRadiantiq
(331)343-LandlineOnvoy
(331)345-LandlineFractel
(331)348-LandlineFractel
(331)356-LandlineFractel
(331)373-LandlineTon80 Communications
(331)385-WirelessNew Cingular Wireless Pcs
(331)388-LandlineFractel
(331)399-LandlineFractel
(331)400-LandlineFractel
(331)401-LandlineLevel 3 Communications
(331)422-LandlineLevel 3 Communications
(331)425-WirelessT-Mobile Usa
(331)426-LandlineTon80 Communications
(331)431-LandlineBandwidth.Com Clec
(331)442-WirelessVerizon Wireless
(331)444-WirelessVerizon Wireless
(331)452-WirelessVerizon Wireless
(331)454-WirelessNew Cingular Wireless Pcs
(331)456-LandlineFirst Communications
(331)457-WirelessVerizon Wireless
(331)462-LandlineXo Illinois
(331)465-WirelessNew Cingular Wireless Pcs
(331)466-LandlineTon80 Communications
(331)472-WirelessT-Mobile Usa
(331)481-WirelessVerizon Wireless
(331)500-LandlineFractel
(331)529-LandlineFractel
(331)551-WirelessNew Cingular Wireless Pcs
(331)575-WirelessSprint Spectrum
(331)588-WirelessNew Cingular Wireless Pcs
(331)600-LandlineFractel
(331)625-WirelessVerizon Wireless
(331)627-LandlineTon80 Communications
(331)631-LandlineOnvoy Spectrum
(331)642-LandlineBandwidth.Com Clec
(331)643-WirelessSprint Spectrum
(331)645-WirelessSprint Spectrum
(331)666-LandlineOnvoy
(331)684-LandlineRcn Telecom Services Of Illinios
(331)688-LandlineTon80 Communications
(331)701-WirelessVerizon Wireless
(331)702-LandlineMcimetro Access Transmission Services
(331)703-WirelessT-Mobile Usa
(331)704-LandlineBandwidth.Com Clec
(331)707-WirelessT-Mobile Usa
(331)716-LandlineOnvoy
(331)717-WirelessNew Cingular Wireless Pcs
(331)725-WirelessNew Cingular Wireless Pcs
(331)732-LandlineFractel
(331)746-LandlineTon80 Communications
(331)757-WirelessT-Mobile Usa
(331)758-LandlineFractel
(331)771-LandlineOnvoy
(331)775-LandlineComcast Ip Phone
(331)777-WirelessVerizon Wireless
(331)788-LandlineFractel
(331)800-LandlineOnvoy
(331)801-LandlineTeleport Communications America
(331)803-LandlinePeerless Network Of Illinois
(331)806-LandlineComcast Ip Phone
(331)808-LandlineBandwidth.Com Clec
(331)814-WirelessT-Mobile Usa
(331)825-LandlineDigital Network Access Communications
(331)826-WirelessSprint Spectrum
(331)837-LandlineTon80 Communications
(331)850-LandlineRadiantiq
(331)866-LandlineTon80 Communications
(331)867-LandlineFractel
(331)871-LandlineOnvoy
(331)888-LandlinePeerless Network Of Illinois
(331)899-LandlineFractel
(331)900-LandlineFractel
(331)901-LandlineBandwidth.Com Clec
(331)903-LandlineAt&T
(331)946-LandlineFractel
(331)979-LandlineComcast Ip Phone
(331)980-WirelessT-Mobile Usa
(331)998-WirelessVerizon Wireless
(331)999-LandlineBandwidth.Com Clec

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, 1,081 unwanted-call complaints were reported to the FTC for numbers showing the 331 code (74% 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, 1,081 unwanted-call complaints were reported to the FTC for numbers showing the 331 code (74% 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, 1,081 unwanted-call complaints were reported to the FTC for numbers showing the 331 code (74% 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 1,703,350 residents. It shares its area with overlay code 630.

When did area code 331 go into service?

Area code 331 went into service on October 7, 2007. It was added as an overlay of 630, so 331 numbers serve the same area that 630 already covered.

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.

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