Knorr replaces Doug Mallory, who was let go earlier this month. The Hoosiers finished last in the Big Ten in total defense for the third straight season under head coach Kevin Wilson, allowing 38.8 points per game in 2013.
Knorr spent the previous three seasons as Wake Forest's defensive coordinator. The Demon Deacons finished 32nd in the FBS in total defense last season.
He also was the head coach at Ohio from 2001-04 and two three-year stints as an assistant coach at Air Force, where he graduated in 1986.