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US area code · Illinois

312 area code

Where the 312 area code is, its overlay and how to dial a +1 312 number from anywhere.

CoversChicago, IllinoisTime zoneCentral (CT)TypeOverlay
Quick answer

The 312 area code is in Chicago, Illinois, United States (Central (CT)). To call from abroad: +1 312 555-0123. It is an overlay, so all 10 digits are dialled.

StateIllinois
Main areaChicago
Time zoneCentral (CT)
TypeOverlay
10-digit dialingRequired
In service since01-Jan-1947

The 312 area code is a geographic North American Numbering Plan (NANP) code covering Chicago, Illinois. It has been in service since 01-Jan-1947 and sits in the Central (CT) time zone.

Overlay 312 shares its region

Several area codes cover the same geographic area, so two neighbours can have different codes. Because of the overlay, you must dial all 10 digits (area code + number) even for local calls.

312872

How to dial a 312 number

From abroad+1 312 555-0123
Within the US / Canada1 312 555-0123
Locally (same area)312 555-0123

Cities in the 312 area code

A 312 number is usually in one of these places in Illinois — 1 county.

West Chicago Dupage

Other Illinois area codes

217224309331447464618630708730773779815847861872

Frequently asked questions

Where is the 312 area code?

The 312 area code is in Chicago, Illinois, United States (Central (CT)).

Is 312 an overlay area code?

Yes. 312 overlays the same region as 872, so callers dial all 10 digits.

Do I have to dial 10 digits for 312?

Yes — dial the area code plus the seven-digit number.

How do I call a 312 number from another country?

Dial your exit code (or +), then 1, then 312, then the number: +1 312 555-0123.

Source: NANPA numbering plan. An area code covers a region, not a precise address — a 312 number does not pinpoint a street or ZIP code.

Number holders in area code 312

Each prefix (the three digits after the area code) is assigned by NANPA to one telephone company. 798 prefixes are in use in 312, shared by 39 companies. The largest holders:

CompanyPrefixesShare
Illinois Bell Tel Co33442%
New Cingular Wireless PCS, LLC8210%
T-Mobile USA, Inc.648%
Cellco Partnership Dba Verizon Wireless547%
Mcimetro Access Transmission Services LLC334%
Spok, Inc.334%

Source: NANPA central office code assignments. A number keeps its original prefix when it is ported to another carrier.

Complaints about 312 numbers

Reports to the FTC, last 30 days
385
Recorded messages or robocalls
46%
Rank among area codes
#253 of 670
Most reported subjects
Other (184)
Dropped call or no message (65)
Reducing your debt (credit cards, mortgage, student loans) (36)

Period Aug 26 – Sep 24, 2026. These are the numbers shown on the caller ID of the reported calls; many are spoofed and do not belong to the real caller.

Source: US Federal Trade Commission, Do Not Call reported calls data (daily files).

All US area codes United States +1 Map of area code 312 — cities & rate centres

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