Karn replaces former coach Mark Montgomery, who resigned in July.
The Terps were ranked early in the season, but just missed out on an NCAA tournament bid. Their roster is poised to look a lot different next year.
The Terps were held to four hits in the season-ending defeat.
The Terps split a doubleheader, falling to BYU before topping the Spartans.
The Terps cruised to a victory after scoring three runs in the opening inning and will play the winner of San José State and BYU on Friday.
The Terps' pitching struggles led them to an exit in the opening round of the conference tournament.
The Terps recorded their most wins since 2011 during the regular season, but still need a strong conference tournament to earn an at-large postseason bid.
The Terps won 36 games this season, the most since 2012.
The pitcher's big day contributed to the Terps clinching their final regular-season series.
Courtney Wyche limited the Fighting Illini's offense throughout the Terps' crucial win.