The Big Twelve Conference is a high school athletic conference in the Illinois High School Association (IHSA), based in Central Illinois. While the name implies that the conference has twelve schools, there are actually only eleven schools currently active, due to other schools either closing, ending offering varsity athletics, or changing conferences. Stephen Decatur High School closed, bringing membership down to eleven. Rantoul High School then left to join the Corn Belt Conference, citing its inability to compete with larger schools.