It dates from the days long ago when almost all police departments in Lake County were on 156.210 and most of the fire departments were on the old 154.400 repeater. Before the ISP put in satellite receivers on ISPERN (in those days on 154.680) it was difficult for Lake County units to hear and be heard by District 2 over in Elgin.
Lake County applied for and was given permission to install an ISPERN base and to accept ISPERN broadcasts for Lake County agencies, which it still does to this day.
Over the years most police departments in Lake County installed independant radio systems, and the State Police has better ISPERN coverage in the area, but many Lake County towns as well as the SO still uses Lake County dispatch for ISPERN broadcasts.
There is some deja vu going on up here as well... Several Lake County towns are now using the Lake County EDACS system for dispatch operations, including Park City, Island Lake and Port Barrington. Wauconda is also supposed to be going as well. Others are looking into it.
My first scanner (Regency 8 Ch VHF) my Dad gave me 35 years ago had crystals for Lake County's channels since he bought it from a LCSO deputy. I listened to it day and night...