Thursday’s forum is hosted by Chicago’s WTTW-TV.
Those expected to attend are Treasurer Dan Rutherford, businessman Bruce Rauner and state Sens. Bill Brady and Kirk Dillard.
GOP candidates have participated in numerous debates statewide, including at Chicago television stations, in Springfield and Peoria.
The primary election takes place on Tuesday. Early voting runs through Saturday.
Gov. Pat Quinn is seeking re-election and faces one primary challenger, activist Tio Hardiman. Quinn’s campaign has said the Chicago Democrat won’t participate in any debates ahead of the primary.