The 1991 Illinois Fighting Illini football team was an American football team that represented the University of Illinois at Urbana-Champaign as a member of the Big Ten Conference during the 1991 NCAA Division I-A football season. In their fourth and final year under head coach John Mackovic, the Fighting Illini compiled a 6–6 record, finished in fifth place in the Big Ten, and outscored opponents by a total of 261 to 182.