Illinois Statutes Chapter 735. Civil Procedure § 5/9-107.5. Notice to unknown occupants

(a) Service of process upon an unknown occupant may be had by delivering a copy of the summons and complaint naming “unknown occupants” to the tenant or any unknown occupant or person of the age of 13 or upwards occupying the premises.

(b) If unknown occupants are not named in the initial summons and complaint and an eviction order in favor of the plaintiff is entered, but the order does not include unknown occupants and the sheriff determines when executing the eviction order that persons not included in the order are in possession of the premises, then the sheriff shall leave with a person of the age of 13 years or upwards occupying the premises, a copy of the order, or if no one is present in the premises to accept the order or refuses to accept the order, then by posting a copy of the order on the premises. In addition to leaving a copy of the order or posting of the order, the sheriff shall also leave or post a notice addressed to “unknown occupants” that states unless any unknown occupants file a written petition with the clerk that sets forth the unknown occupant's legal claim for possession within 7 days of the date the notice is posted or left with any unknown occupant, the unknown occupants shall be evicted from the premises. If any unknown occupants file such a petition, a hearing on the merits of the unknown occupant's petition shall be held by the court within 7 days of the filing of the petition with the clerk. The unknown occupants shall have the burden of proof in establishing a legal right to continued possession.

(c) The plaintiff may obtain an eviction order only and not for rent as to any unknown occupants.

(d) Nothing in this Section may be construed so as to vest any rights to persons who are criminal trespassers, nor may this Section be construed in any way that interferes with the ability of law enforcement officials removing persons or property from the premises when there is a criminal trespass.