Published: October 29, 2019
Central Illinois' counties and cities currently using area code 217 will soon be served by a second area code. The new 447 area code, scheduled to enter service in 2021, will overlay NPA 217, covering the same geographic area. Some larger cities affected are: Champaign, Decatur or the state's capital Springfield.
As a result, 10 digit dialing will be mandatory for all local calls within the newly created overlay complex 217/447, while toll calls will require 1+10 digit dialing.
More info in the official announcement from NANPA (North American Numbering Plan Administrator) (PDF document).
Visit area code 447 page for a list of cities served, map and other info.