Candidate Julie Hamos is a state representative, Dan Seals is a consultant who ran two losing campaigns against Kirk, and Elliot Richardson is an attorney.
Among the issues discussed Sunday afternoon were jobs, campaign finance reform and dealing with terrorism.
Richardson and Hamos advocated strong sanctions on Iran.
"We have to respond very forcefully with strong sanctions. The strong sanctions are before Congress, and we need to make sure they're not just passed this time but actually enforced," Hamos said.
"We need tough, serious sanctions against Iran, and we need to start now," said Richardson.
"We also have to put more effort into stopping and finding the conditions that cause terrorism. In my mind, that is a lack of education, that is poverty, and that is government's support of injustice," Seals said.
There are five Republicans campaigning to succeed Kirk in the district.