The 1989 Illinois High School Association (IHSA) State Championship Tournament was held in May, 1989 at Mahomet-Seymour High School. It was the third State Championship Tournament in Illinois, sponsored by the IHSA.
The state was divided into 16 areas, termed in Illinois as Sectionals. Each sectional hosted a tournament, the winner of which advanced to the State Tournament. The determination of these geographic boundaries was arbitrarily decided by the IHSA Office.
Each round was comprised of 30 toss-ups and accompanying bonus questions (10 fewer per round than from the first two years of the tournament). The sectional tournaments and State Championship Tournament were all single elimination. Teams were randomly assigned to positions in the bracket without regard for record or performance.
There was no third place match. The top two teams earned trophies and medals for team members, coaches, principals, and activities directors. The trophies were of the design smaller than that of the athletic trophies given out by the IHSA.
- Sullivan became the first team to defeat Quincy in this tournament after Quincy had swept the previous two titles.
- Quincy's octafinal win gave it nine consecutive wins in this tournament. As of 2008, this consecutive wins marks has only been surpassed by IMSA's 17 (1994, 96-99), Latin's 15 (2003-07), and Wheaton North's 14 (2002-2005).
- This was the first of IMSA's eight state titles.
- The coach of Breese Central, Robert Pierce, would go on to found Answers Plus, which would eventually provide questions to the IHSA for its State Series.
- Sullivan would finish second at the NAC.