| 1885 | Chicago (Lake View) beats Chicago (South Division) in the first known football game between Illinois high schools. |
| 1974 | First state football playoffs conducted; finals in five classes held at Hancock Stadium on the campus of Illinois State University, Normal. |
| 1980 | Playoffs expanded to six classes. |
| 1981 | Class 5A and 6A title games moved to Dyche Stadium on the campus of Northwestern University, Evanston. |
| 1985 | Playoffs expanded from 16 teams to 32 teams in each class; class 5A and 6A games returned to Hancock Stadium. |
| 1991 | "Football enrollment" concept established, taking into account enrollments of scheduled opponents. |
| 1994 | Playoffs seeded for the first time; quadrants used to group teams; Wednesday playoff game eliminated. |
| 1996 | Some classes seeded in halves or as a single group for the first time. |
| 1999 | Championship games moved to Memorial Stadium, Champaign. |
| 2001 | Playoffs expanded to eight classes of 32 teams each. |
| 2002 | All classes seeded in quadrants to reduce travel. |
| 2006 | Some classes seeded in halves again. |
| 2007 | "Football enrollment" concept eliminated. |