The Illinois State Police and many other agencies have switched to the statewide StarCom21 digital trunked radio system. The system operates on the 700 and 800 MHz. bands and can be monitored with several models of
digital police scanners
In the Chicago area, the Cook County Sheriff uses an encrypted digital Motorola Type II trunked radio system although some operations are unencrypted. Chicago Police use an analog UHF repeater system that can be monitored on a basic police scanner. The Chicago Fire Department uses several analog VHF and UHF channels that can be monitored with a basic police scanner but will transition to a digital UHF radio system that would require a
digital police scanner.
Suburban counties use a variety of radio system types. Will County and Lake County use EDACS trunking systems, DuPage County uses non-trunked 800 MHz. channels, and DeKalb, Kane and McHenry Counties use analog VHF channels. McHenry County will transition to a StarCom21 system soon however so a
digital police scanner will be needed.
In the suburbs most agencies use UHF or VHF analog systems. Some 800 MHz. analog and digital systems are in use in the far Northwest suburbs (Arlington Hts., Schaumburg, Palatine etc.)
Downstate some areas use StarCom21, including McLean, St. Clair and Madison Counties. Champaign County uses a digital trunked radio system that uses some encryption. Each of these require a
digital police scanner. Other locations use mostly VHF channels and some UHF channels that can be heard on a basic police scanner.