The 312 area code is located in the state of Illinois, and according to Intelius data, covers roughly 484,344 phone numbers and 604,719 listings across 792 prefixes.
This is a General Purpose Code, in service since January 1, 1947.
Area code 312 is part of an overlay complex shared with:
Local and long-distance calls within area code 312 both require 1 plus 10 digits dialing.
Have you received a call from a number with a 312 area code? Figure out who is calling you by performing a reverse phone lookup search. Intelius can provide you with a phone report that includes (when available) original line type and carrier, the number owner’s name, last known address and past addresses, age, possible relatives, and more.
| County Population (2025) | 5,194,625 |
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