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331 Area Code

Area Code Overview

Area code 331 is a geographic telephone area code in Illinois that went into service on October 7, 2007. The geographic regions covered by this area code overlay has a population of approximately 4,270,814.

Overlay and Dialing Rules

  • Area Code: 331
  • State: Illinois
  • Type: General Purpose Code
  • In Service Date: October 7, 2007
  • Overlay Complex: 331/630
  • Local Dialing Plan: This area requires you to dial 1 and the area code when calling locally.

Estimated Number of Assigned Phone Numbers in Area Code 331

This area code is ranked 286th out of 363 nationwide in estimated assigned phone numbers. Within the state territory it serves, it is ranked 13th out of 16.

2,084,000

Estimated Service-Type Mix of Assigned Phone Numbers in Area Code 331

Total assigned 2,084,000
Wireless
849,000 assigned
40.74%
Wireline and VoIP
1,082,000 assigned
51.92%
Other / Unclassified
153,000 assigned
7.34%

Estimated Share of Wireless Numbers Originally Assigned to Each Carrier in Area Code 331

Estimated assigned wireless phone numbers: 849,000

Numbers may later be ported to another carrier, but this chart reflects original number assignment, not current subscriber share.

AT&T Wireless 295,000 (34.75%)
T-Mobile 295,000 (34.75%)
Verizon Wireless 259,000 (30.51%)

Estimated Share of Wireline and VoIP Numbers Originally Assigned to Each Carrier in Area Code 331

Estimated assigned wireline and VoIP phone numbers: 1,082,000

Onvoy 483,000 (44.64%)
Bandwidth 159,000 (14.70%)
Spectrum 69,000 (6.38%)
Comcast Business 61,000 (5.64%)
Peerless Network 61,000 (5.64%)
Lumen 58,000 (5.36%)
Commio 44,000 (4.07%)
AT&T 30,000 (2.77%)
MCIMETRO ACCESS TRANSMISSION SERVICES LLC - IL 27,000 (2.50%)
Telnyx 27,000 (2.50%)
Vonage 22,000 (2.03%)
PAETEC ITEL, LLC 17,000 (1.57%)

Other / Unclassified Assigned Numbering in Area Code 331

Estimated assigned other or unclassified phone numbers: 153,000

TELEPORT COMMUNICATIONS AMERICA, LLC - IL 34,000 (22.22%)
IP HORIZON LLC 26,000 (16.99%)
FRACTEL, LLC 25,000 (16.34%)
FIRST COMMUNICATIONS, LLC 18,000 (11.76%)
STRATUS NETWORKS 18,000 (11.76%)
TON80 COMMUNICATIONS, LLC 11,000 (7.19%)
DIGITAL NETWORK ACCESS COMMUNICATIONS, INC. - IL 10,000 (6.54%)
ACCESS ONE, INC. - IL 5,000 (3.27%)
HD CARRIER LLC 4,000 (2.61%)
CLEAR RATE COMMUNICATIONS, LLC 2,000 (1.31%)

Cities and Towns in Area Code 331

Aurora, Illinois Bartlett, Illinois Batavia, Illinois Bensenville, Illinois Big Rock, Illinois Chicago, Illinois Downers Grove, Illinois Elburn, Illinois Elgin, Illinois Elmhurst, Illinois Geneva, Illinois Glen Ellyn, Illinois Hinsdale, Illinois Itasca, Illinois Kaneville, Illinois La Grange, Illinois Lemont, Illinois Lombard, Illinois Maywood, Illinois Naperville, Illinois Northbrook, Illinois Oswego, Illinois Plano, Illinois Roselle, Illinois St. Charles, Illinois Sugar Grove, Illinois Summit, Illinois Warrenville, Illinois West Chicago, Illinois Western Springs, Illinois Wheaton, Illinois Wheeling, Illinois Yorkville, Illinois

These geographic regions are also served by area code 630.

How These Figures Were Built

These figures are estimates based on public phone-number assignment records. They are meant to show the likely mix of assigned phone numbers associated with area code 331, not live customer counts.

Some providers may have assigned phone numbers tied to this area code even if they do not actively market or sell service locally. These figures reflect public number-assignment records, not confirmed local service availability.

They also do not reflect number portability at the individual phone-number level, so some numbers may now be used on a different network or by a different provider than the original assignment records suggest.

Population data and locality matching provided by GeoNames.

Last refreshed: April 15, 2026 6:22 pm