The 2004–05 Illinois Fighting Illini men's basketball team marked the 100th season of men's basketball at the University of Illinois at Urbana–Champaign. After starting the regular season with a record of 29–0 and winning the Big Ten Conference regular season title outright at 15–1, the Illini were Big Ten tournament champions. They advanced in the NCAA tournament to the national championship, marking the school's first appearance in the championship game, but lost to North Carolina, 75–70. They ended the season at 37–2, tying the record for most victories in a season for a men's college basketball team.

The Illinois Fighting Illini men's basketball team is an NCAA Division I college basketball team competing in the Big Ten Conference, that represent the University of Illinois Urbana-Champaign. Home games are played at the State Farm Center, located on the University of Illinois Urbana-Champaign's campus in Champaign. Illinois has one pre-tournament national championship and one non-NCAA tournament national championship in 1915 and 1943, awarded by the Premo-Porretta Power Poll. Illinois has appeared in the NCAA Division I men's basketball tournament 34 times, and has competed in 5 Final Fours, 10 Elite Eights, and has won 18 Big Ten regular season championships, and 4 Big Ten Tournament Championships.