The 2005 Illinois High School Association (IHSA) State Championship Tournaments ended the nineteenth State Championship Series conducted in Scholastic Bowl by the IHSA. It was the fourteenth season in which there were separate State Championship Tournaments held for small schools (Class A) and large schools (Class AA). For the ninth year, both tournaments were held at the Peoria Civic Center.
Teams were assigned to one of eight sectionals within each class. Teams were seeded by the coaches, and teams would then be assigned to one of four Regionals within each Sectional. The winners of the regionals would advance to their respective sectional tournaments, where they would play a three match round robin to determine a winner. The determination of the geographic boundaries of the Sectional was arbitrarily decided by the IHSA Office.
Each round was comprised of 30 toss-ups and accompanying bonus questions.
In the State Championship Tournament, teams would be randomly assigned to pools of four, and play a three match round robin. The winners of each pool would advance to the Championship Match, and the runners-up in each pool would advance to play for third place. Ties were broken by head-to-head results or total points scored (in the event of a three way tie)
The top four 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.
For the fifth year, the questions were written by a group of retired coaches and person from other states.
Eureka swept through their pool with a 3-0 record. St. Teresa went 2-1 to advance to the third place match.
The Latin School swept through their pool with a 3-0 record. Marquette went 2-1 to advance to the third place match.
Stevenson swept the pool to advance to the Championship Match. Auburn went 2-1 and advance to play for third place.
Wheaton North swept the pool to advance to the Championship Match. Deerfield went 2-1 and advance to play for third place.
- The third round Class A match between St. Teresa and Riverdale marked the first time in Tournament history that neither team was able to score 100 points.
- Stevenson ended the three year reign of Wheaton North, winning their second state title.
- The surprise non-attendee was MacArthur and their senior star Donald Taylor. There was controversy that erupted when, at the Sectional Tournament hosted by Carbondale, the scoreboard showed MacArthur leading Carbondale by five points going in to the final question. After Carbondale answered incorrectly, Taylor intentionally rang in with the incorrect answer to kill the question, and prevent the possibility of Carbondale sweeping a rebounded bonus. Only after the match was completed was it learned that the scoreboard was in err, and that Carbondale was actually ahead by five points. Carbondale won the final match, and advanced to the State Championship Tournament.