The 331 area code is located in the state of Illinois, and according to Intelius data, covers roughly 28,861 phone numbers and 32,796 listings across 217 prefixes.
This is a General Purpose Code, in service since October 7, 2007.
Area code 331 is part of an overlay complex shared with:
Area code 331 was split from area code 630.
Local and long-distance calls within area code 331 both require 1 plus 10 digits dialing.
Have you received a call from a number with a 331 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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| County Population (2025) | 934,298 |
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| County Population (2025) | 525,757 |
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| County Population (2025) | 712,253 |
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