Horn graduated from Athol Murray College of Notre Dame in 1985 and was recruited by Bill Wilkinson to play for Western Michigan. He became the team's starter as a freshman, taking over after the graduation of Glenn Healy, and backstopped the team to their best season in history. Horn set a program record and led the nation with 25 wins, helping WMU win 32 games that year (the only 30-win season for the program as of 2021). Horn played well during the regular season, helping the team finish in a second place tie in the CCHA, but it was in the playoffs where he became a star. While WMU had been led by their powerful offense, Horn kept his team in the semifinal against Bowling Green, winning the game in overtime. He then held top-seeded Michigan State to a single goal to claim the team's first conference championship (the Broncos would not win another for 26 years). Horn was named the Tournament MVP and led his team to their first ever NCAA Tournament appearance. While the team was swept out of the quarterfinals, Horn received a fair bit of notoriety from his performance and was drafted by the Hartford Whalers in the succeeding NHL Draft.