Prefix 312-631 — Chicago Zone 01, IL

NANPA CO code assignment, current as of July 28, 2026.

312-631 identifies a block of numbers in Chicago Zone 01, IL, within the 312 area code. Every US prefix is tied to exactly one rate center; this one is Chicago Zone 01.

The rate center lies in the Chicago-Naperville-Elgin, IL-IN Metropolitan Statistical Area. The serving LATA is 358. Local time follows the Central zone.

Treat the on-screen number as a hint, not evidence — 312-631 can be spoofed like any US prefix. If a call feels off, verify through an official callback number and file a complaint with the FCC or FTC.

Code-holder of record: CENTURYLINK COMMUNICATIONS, LLC (OCN 508J), assigned January 11, 2013. The prefix is pooled: its ten thousands-blocks can be shared among several carriers, so different 312-631 numbers may be served by different companies.

Neighboring prefixes

FAQ

Where is 312-631 located?

The prefix is assigned to the Chicago Zone 01 rate center in IL, area code 312. It is part of the Chicago-Naperville-Elgin, IL-IN Metropolitan Statistical Area.

Which company owns 312-631 numbers?

CENTURYLINK COMMUNICATIONS, LLC holds the code, but the prefix is pooled — individual thousands-blocks can be assigned to other carriers, and numbers may be ported to any provider.

Is a call from 312-631 safe to answer?

The prefix itself says nothing about the caller. Legitimate Chicago Zone 01 businesses and spoofed robocalls can both display it. Never share personal data with an unverified inbound caller.