755 ILCS 20/4
All persons, bodies, politic and corporate, named in such complaint as having possession rights or claimants of the estate, may appear and plead to such proceedings, and may deny the facts stated in the complaint, and the title of the county to the lands and tenements therein mentioned, at any time on or before the third day after the return day of the order, and any other person claiming an interest in such estate may appear and be made a defendant and plead to the complaint, by motion or by answer, within the time allowed for pleading; and if no person appears and pleads, or appearing, refuses to plead within the time, then judgment shall be entered vesting title in the county to the lands and tenements in such complaint claimed; but if any person appears and denies the title set up by the county, or denies any material facts in the complaint, an issue or issues shall be made up and tried as other issue of facts, and a survey may be ordered and entered as in other actions where the title or boundary of lands is drawn in question; and if, after the issues are tried, it appears from facts found or admitted that the county has good title to the lands and tenements in the complaint mentioned, or any part thereof, judgment shall be entered vesting title thereof in the county, and the county shall recover costs of the action against the defendant or defendants.
755 ILCS 20/4