|Basketball invented at Springfield, Mass., by James Naismith.
|Chicago (Morgan Park Academy) becomes first Illinois secondary school to organize a boys basketball team.
|Chicago (Englewood) defeats Elgin (H.S.) in the first known boys basketball game between Illinois high schools.
|Team from Chicago (North Division) plays in exhibition tournament of high school basketball teams at St. Louis Olympics.
|Lewis Omer, athletic director of Oak Park (O.P.-River Forest), gains IHSAA approval to organize first state high school basketball tournament, an invitational meet held at Oak Park YMCA; Peoria (H.S.) defeats Rock Island (H.S.) in title game.
|IHSAA assumes administration of tournament and opens it to all member schools; state final tournament moved to Bloomington YMCA; six district tournament champions and six runners-up advance to state final.
|State final field reduced to six teams as district champions only allowed to advance.
|State final tournament moved to Bradley Gym in Peoria.
|State final tournament moved to Decatur YMCA.
|State final tournament returned to Bradley Gym.
|State final tournament returned to Decatur YMCA; state final field expanded to eight teams.
|State final tournament moved to Millikin Gym in Decatur.
|State final field expanded to 11 teams.
|State final field expanded to 12 teams.
|State final tournament moved to Springfield H.S.; state final field expanded to 13 teams.
|After eleven years at various sites, state final tournament moved to campus of University of Illinois at Urbana-Champaign; games played at Men's Gym Annex (now known as Kenney Gym).
|State final field expanded to 16 teams.
|Cumbersome field of 21 district tournament winners qualifies for state finals; at end of school year, Charles Whitten hired as IHSAA's first executive secretary and given duty of reorganizing tournament.
|Sectional tournament stage added between district and state final; state final field reduced to four teams.
|Elgin (H.S.) becomes first school to win back-to-back state titles.
|State final tournament moved to Huff Gym.
|State final field expanded to eight teams; Cicero (Morton) wins national championship tournament at University of Chicago (after being eliminated in sectional during state tournament).
|Chicago Public League teams enter state tournament for first time.
|State final field expanded to sixteen teams, known as "Sweet Sixteen."
|Regional tournament stage added between district and sectional; lowest-rated teams in each area required to play in district tournament; district and regional runners-up allowed to advance to next stage.
|Chicago Public League champion given automatic berth in the state final tournament.
|First tournament played under new rule eliminating center jump after each field goal; district tournament definition changed so that smallest schools in each area, rather than the lowest-rated schools, required to play in district tournament.
|IHSAA assistant executive secretary H.V. Porter coins the term "March Madness" to describe state basketball tournament.
|IHSAA (Illinois High School Athletic Association) becomes IHSA (Illinois High School Association).
|In one-year experiment, state final field reduced to four teams; first-round and quarterfinal games held at four sites; private schools allowed to join IHSA and enter tournaments; Chicago Public League refuses to send champion to state final in dispute over new IHSA constitution.
|Segregated schools of southern Illinois, never allowed to participate in the state tournament, invited to stage conference championship game prior to the first quarterfinal game at Huff Gym.
|District and regional runners-up no longer allowed to advance to next stage.
|Taylorville becomes first known undefeated state champion.
|Segregated schools of southern Illinois allowed to compete in state tournament; special conference championship game discontinued.
|State final carnival held for first time.
|Hebron becomes only district (small) school to win state championship; first live television coverage of state final (semifinals and title game).
|State final field reduced to eight teams, known as "Elite Eight"; first-round games of state final played at eight super-sectional sites.
|Chicago (Marshall) becomes first Chicago school to win state basketball title.
|State final tournament moved to Assembly Hall.
|Tournament split into Class A (small schools), won by Lawrenceville, and AA (large schools), won by Dolton (Thornridge); district tournament stage eliminated; two state finals held on consecutive weekends at Assembly Hall; state final carnival discontinued.
|Chicago Catholic League teams enter state tournament for first time.
|First tournament played under new rule allowing three-point field goal.
|In only triple-overtime championship game, East St. Louis (Lincoln) becomes first school to win three consecutive state titles.
|Class AA teams seeded in sectional complexes instead of at the regional stage; regional games played on court of higher seed.
|"Happening" three-point and slam-dunk contests held for first time; state final reunions held for first time.
|After 77 years at the University of Illinois, state final tournament moved to Peoria Civic Center; March Madness Experience held for first time; reunions discontinued.
|Peoria (Manual) becomes first school to win four consecutive state championships.
|Chicago Public League champion no longer given automatic berth in
Class AA state finals; Public League teams enter tournament at regional level in
either Class A or Class AA; Class AA teams seeded in modified sectional complex with fixed regional sites.
|Class A teams seeded in modified sectional complex with fixed regional
sites, divided into two sub-sectionals.
|Some Class AA sectionals seeded in two sub-sectionals.
|Tournaments cancelled due to COVID-19 pandemic.
|State final tournament moved back to Champaign, State Farm Center. Tournaments not held due to COVID-19 pandemic.