Big 8 Conference... Vincennes Lincoln, Princeton, Washington, Boonville, Jasper, Mt Vernon (Posey), and Mt Carmel, IL (the southern Illinois city, not the Chicago Catholic School). The are all 3A football schools except Jasper, which is 4A.
TH North and South were in the SIAC until some time in the 80's and they dropped out. They are the only 5A schools in their area, so they'll have to travel no matter what conference they belong to.
Vincennes Lincoln and North Knox offer wrestling, while Vincennes Rivet and South Knox do not.