Illinois State battled back from a 17-point deficit to claw within 3 points several times, but could not overcome the Jayhawks and 31 points from Danielle McCray.
The 75-72 victory launched Kansas (22-13) into its first Postseason WNIT championship game.
Illinois State (27-8), which won three postseason games for the first time in school history, won at least 25 games for the second consecutive season.
Kansas will play South Florida in the WNIT championship game beginning at 2 p.m. ET Saturday, April 4. The game will be broadcast live on CBS College Sports.
South Florida (26-10) took control of a close game early in the second half Wednesday night to defeat host Boston College (23-12) 82-65. It's the second straight road win for South Florida. The Bulls, who have won eight of their last nine games, continue to add to their school record for wins.
Wednesday, April 1
South Florida 82, Boston College 65
Kansas 75, Illinois State 72
Saturday, April 4
South Florida at Kansas, 2 p.m. ET