List of Illinois area codes

With the depletion of new numbers in area codes 312 and 773, an overlay of both of them, area code 872, was created in November 2009, beginning ten-digit dialing within the city limits of Chicago.

Downstate, no changes took place from 1957 until 2021, when area code 447 was implemented as an overlay with 217, mandating ten-digit dialing.

The remainder of the state switched to ten-digit dialing in October 2021, as a result of the implementation of the 988 Suicide & Crisis Lifeline.

[1][2] Area code 730 went into effect on July 7, 2023, as an overlay complex with 618.

As of that date, all numbering plan areas of Illinois are therefore overlays.