It may not have the same ring as the Original Six, but below are two of the oldest IHSA documents in existence, which list the first 27 members of what was originally called “The Illinois High School Athletic Association."

The first document lists the IHSA member schools as of September 1, 1905 (note that De Kalb, El Paso and Forrest are misspelled).

An unknown individual has penciled in numbers to put the schools in alphabetical order. The complete list is:
1-Alton                 12-Kewanee
2-East Aurora       13-Lincoln
3-West Aurora      14-Moline
4-Bloomington      15-Ottawa
5-Centralia           16-Princeton
6-De Kalb             17-Quincy
7-Elgin                 18-Rockford
8-El Paso             19-Rock Island
9-East St. Louis    20-Springfield
10-Forrest              21-Streator
11-Joliet                22-Danville

The second document is a list of member schools that accompanied a letter to principals in December, 1906 encouraging them to join the Association. The schools that were added in the 15 months between the two letters were Hoopeston, Rochelle, Jacksonville, Geneva and Plainfield.