That news was learned Monday night when the women's bracket was released.
The two will play at noon CDT at West Lafayette, Ind.
The winner will play the victor between No. 5 seed Notre Dame and No. 12 seed Southern Methodist. The second-round game will be played next Tuesday in West Lafayette.
Illinois State, a No. 13 seed, enters with a 26-6 record and was the Missouri Valley Conference regular season and tournament champion. This is the Redbirds' fifth trip to the Big Dance, but first since 2005.
They are on a four-game win streak after losing three straight in late February and early March.
Oklahoma is 21-8 and is coming off three straight losses, the most recent a 70-64 defeat to Missouri in the opening round of the Big 12 Tournament.
Oklahoma City's Ford Center will host a regional March 29-April 1. During those two rounds, teams nationwide will be narrowed down from 16 to the Final Four.
This year's Women's Final Four takes place in Tampa, Fla.