The conference origins date back to 1925 with charter schools that included; Bloomington, Champaign, Danville, Stephen Decatur, Lincoln, Jacksonville, Mattoon, Pekin, Peoria Central, Peoria Manual, Springfield, and Urbana.
In 1983, the conference morphed again with the departure of Springfield High School and the addition of Champaign Centennial, Decatur Eisenhower, Decatur MacArthur, Normal Community, and Rantoul, bringing the total number of teams back to 12.
The league transitioned into a two-division, East-West format with Centennial, Central, Danville, Mattoon, Rantoul and Urbana in the East and Bloomington, Decatur, Eisenhower, MacArthur, Lincoln, and Normal in the West.
Rantoul departed in 2004, Mattoon left in 2012 and both Decatur schools, Eisenhower and MacArthur followed suit in 2013.
Champaign Central, Danville, and Urbana are the only continuous members to have stayed in the conference since its inception.