The 26 high schools included; Bloom, Bradley, Bremen, Crete-Monee, Eisenhower, Evergreen Park, Hillcrest, Homewood-Flossmoor, Kankakee Eastridge, Kankakee Westview, Lincoln-Way, Oak Forest, Oak Lawn, Reavis, Rich Central, Rich East, Rich South, Richards, Sandburg, Stagg, Thornridge, Thornton, Thornton Fractional North, Thornton Fractional South, Thornwood, and Tinley Park.

Argo moved over from the Illini 8 in 1977 and the same year, Victor J. Andrew High School opened, taking the total number of teams to 30 to close out the 1970's.

[5][6] Bloom Trail would leave the league in 1995, however, Lincoln-Way East would open their doors in 2001, joining the conference in the process.

[7] The conference covered a large geographic area and sociological spectrum "from the Indiana border to Joliet, from impoverished Ford Heights to affluent Frankfort, from virtually all-black Hillcrest to almost all-white Lincoln-Way Central and from Joliet, enrollment 4,993, to 1,066- student Rich South"[7] In 2004, the athletic directors voted 30–3, the principals' board of control voted 6–2, and the district superintendents voted 16–3 to approve a new conference realignment which was to take effect in 2006.

[8] Shortly after the announcement, a board member from Lincoln-Way Community High School District, a district representing two of the schools leaving to form a new conference, was forced to resign after racially insensitive statements were left on a reporter's voice mail.

In April 2006, a federal civil rights lawsuit was filed against the schools which had left claiming that "(an) apartheid-like realignment used public funds to regress to separate but equal".