765 ILCS 45/16
The judgment of the court, when entered, shall be forever binding and conclusive: Provided, that any judgment shall be subject to be opened, modified, vacated or set aside on appeal. Any judgment entered upon any petition or cross-petition, which does not make defendant, by name, all persons who shall be in possession of such lands, or any part thereof at the time of the filing of such petition, or which does not make defendant, by name, all persons to whom any such lands shall have been conveyed, and the deed or deeds of such conveyance shall have been recorded in the office of the recorder of such county since the time of the destruction of the records, as aforesaid, and prior to the time of the filing of any such petition, shall be absolutely void as to such person omitted, but shall be final and conclusive as to all others. All defendants who shall not be actually served with a summons in the action in which such judgment may be entered, shall have allowed to them the same time after the entry of such judgment within which, upon petition to the court entering the judgment, to have such judgment vacated and set aside in the same manner as is allowed to defendants in other civil cases.
765 ILCS 45/16