State party chairwoman Judy Baar Topinka says Republicans will then choose between Alan Keyes and Andrea Grubb Barthwell.
The GOP candidate will take on Barack Obama, a state senator from Chicago and Democratic rising star.
Keyes is a two-time presidential candidate from Maryland. He's never lived in Illinois.
Barthwell is a former deputy drug czar in the Bush administration. She's a physician from the Chicago suburb of River Forest.
Republicans have struggled to find a replacement candidate since Jack Ryan dropped out over embarrassing allegations in his divorce records.