Area Code Overview

Area code 312 is a geographic telephone area code in Illinois that went into service on January 1, 1947. The geographic regions covered by this area code overlay has a population of approximately 2,792,539.

Overlay and Dialing Rules

Area Code: 312
State: Illinois
Type: General Purpose Code
In Service Date: January 1, 1947
Overlay Complex: 312/773/872
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 312

This area code is ranked 27th out of 363 nationwide in estimated assigned phone numbers. Within the state territory it serves, it is ranked 3rd out of 16.

6,825,000

Estimated Service-Type Mix of Assigned Phone Numbers in Area Code 312

Total assigned 6,825,000

Wireless

2,257,000 assigned

33.07%

Wireline and VoIP

3,718,000 assigned

54.48%

Other / Unclassified

850,000 assigned

12.45%

Estimated Share of Wireless Numbers Originally Assigned to Each Carrier in Area Code 312

Estimated assigned wireless phone numbers: 2,257,000

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

T-Mobile 904,000 (40.05%)

AT&T Wireless 822,000 (36.42%)

Verizon Wireless 530,000 (23.48%)

Optimum Mobile 1,000 (0.04%)

Estimated Share of Wireline and VoIP Numbers Originally Assigned to Each Carrier in Area Code 312

Estimated assigned wireline and VoIP phone numbers: 3,718,000

AT&T 2,341,000 (62.96%)

Lumen 287,000 (7.72%)

Bandwidth 273,000 (7.34%)

Onvoy 272,000 (7.32%)

MCIMETRO ACCESS TRANSMISSION SERVICES LLC 180,000 (4.84%)

PAETEC ITEL, LLC 106,000 (2.85%)

MCIMETRO ACCESS TRANSMISSION SERVICES LLC - IL 77,000 (2.07%)

Peerless Network 60,000 (1.61%)

Spectrum 44,000 (1.18%)

Comcast Business 38,000 (1.02%)

RCN TELECOM SERVICES OF ILLINIOS, INC. - IL 21,000 (0.56%)

NUSO 7,000 (0.19%)

Other / Unclassified Assigned Numbering in Area Code 312

Estimated assigned other or unclassified phone numbers: 850,000

SPOK, INC. 340,000 (40.00%)

TELEPORT COMMUNICATIONS AMERICA, LLC - IL 179,000 (21.06%)

AMERICAN MESSAGING SERVICES, LLC 140,000 (16.47%)

FIRST COMMUNICATIONS, LLC 134,000 (15.76%)

ACCESS ONE, INC. - IL 25,000 (2.94%)

INDIANA PAGING NETWORK, INC. 20,000 (2.35%)

HD CARRIER LLC 2,000 (0.24%)

IP HORIZON LLC 2,000 (0.24%)

U.S. TELEPACIFIC CORP. DBA TPX COMMUNICATIONS 2,000 (0.24%)

AIRESPRING, INC. 1,000 (0.12%)

CLEAR RATE COMMUNICATIONS, LLC 1,000 (0.12%)

FRACTEL, LLC 1,000 (0.12%)

Cities and Towns in Area Code 312

Chicago, Illinois Hinsdale, Illinois La Grange, Illinois Northbrook, Illinois Roselle, Illinois Wheeling, Illinois

These geographic regions are also served by area codes 773 and 872.

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 312, 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