331 area code — Aurora, IL geographic

Data: NANPA public reports, current as of July 28, 2026.

If a call shows area code 331, the number was issued in the Aurora area — a code active since 2007, on Central time. Together with 630 it forms the 331/630 overlay. Because of number portability and VoIP, the area code tells you where the number was issued, not where the caller is right now.

NANPA lists 221 active NXX prefixes in 331, assigned to 25 carriers. 220 of those prefixes are pooled — shared between carriers in thousands-number blocks. The code spans 24 rate centers (billing localities).

Official projections put exhaust for the 331/630 complex at 1Q 2080.

Its parent code is 630, which it left in 2007.

The dialing plan is 1+10D for home-NPA local calls and 1+10D across codes.

Practical takeaway: the 331 label narrows geography to Illinois, the prefix narrows it to a locality, and neither authenticates a caller. Verification means calling back through a number you found yourself.

Largest localities in 331

FAQ

Why do 630 and 331 cover the same place?

They are overlays: when a code runs low on numbers, a new code is added over the same territory instead of splitting it. The 331/630 complex shares one service area, and local calls are dialed with 10 digits.

Will 331 run out of numbers?

NANPA's current forecast projects exhaust in 1Q 2080 — decades of capacity remain.

Why am I getting spam calls from 331 numbers?

Scammers spoof recognizable area codes so calls look local or familiar. A displayed 331 number does not prove the call originated there — see our guide to spotting spoofed calls.

Where is a 331 number from?

331 is assigned to Aurora and surrounding areas of Illinois in the Central time zone. The three digits after the area code (the prefix) narrow it down to a rate center.

Is 331 a toll-free number?

No. 331 is a geographic code; calls are billed like any other domestic call. Toll-free codes are 800, 833, 844, 855, 866, 877 and 888.