The conference comprised 15 small public high schools, with enrollments between 60 and 340 students in Iroquois, LaSalle, Livingston, McLean, Tazewell, and Woodford counties.
The first year of competition for the Mid State was 1949 with eight charter schools: Chenoa, Cornell, El Paso, Fairbury, Flanagan, Gridley, Lexington and Minonk-Dana.
In 1992, Minonk-Dana-Rutland consolidated with a neighboring districts Toluca, and Wenona to become known as Fieldcrest, but remained in the Mid State.
For over 40 years the Mid State Conference maintained seven or eight schools with very few exceptions, however in 1995, Cullom Tri-Point and Tremont joined the league taking the total to 10.
In the early 2000s, talks began to join forces with the Sangamon Valley Conference in order to create a league with divisions based on enrollment.