735 ILCS 5/9-107
If the plaintiff, his or her agent, or attorney files an eviction action, with or without joinder of a claim for rent in the complaint, and is unable to obtain personal service on the defendant or unknown occupant and a summons duly issued in such action is returned without service stating that service can not be obtained, then the plaintiff, his or her agent or attorney may file an affidavit stating that the defendant or unknown occupant is not a resident of this State, or has departed from this State, or on due inquiry cannot be found, or is concealed within this State so that process cannot be served upon him or her, and also stating the place of residence of the defendant or unknown occupant, if known, or if not known, that upon diligent inquiry the affiant has not been able to ascertain the defendant's or unknown occupant's place of residence, then in all such eviction cases whether or not a claim for rent is joined with the complaint for possession, the defendant or unknown occupant may be notified by posting and mailing of notices; or by publication and mailing, as provided for in Section 2-206 of this Act. However, in cases where the defendant or unknown occupant is notified by posting and mailing of notices or by publication and mailing, and the defendant or unknown occupant does not appear generally, the court may rule only on the portion of the complaint which seeks an eviction order , and the court shall not enter judgment as to any rent claim joined in the complaint or enter personal judgment for any amount owed by a unit owner for his or her proportionate share of the common expenses, however, an in rem judgment may be entered against the unit for the amount of common expenses due, any other expenses lawfully agreed upon or the amount of any unpaid fine, together with reasonable attorney fees, if any, and costs. The claim for rent may remain pending until such time as the defendant or unknown occupant appears generally or is served with summons, but the eviction order shall be final, enforceable and appealable if the court makes an express written finding that there is no just reason for delaying enforcement or appeal, as provided by Supreme Court rule of this State.
Such notice shall be in the name of the clerk of the court, be directed to the defendant or unknown occupant, shall state the nature of the cause against the defendant or unknown occupant and at whose instance issued and the time and place for trial, and shall also state that unless the defendant or unknown occupant appears at the time and place fixed for trial, judgment will be entered by default, and shall specify the character of the judgment that will be entered in such cause. The sheriff shall post 3 copies of the notice in 3 public places in the neighborhood of the court where the cause is to be tried, at least 10 days prior to the day set for the appearance, and, if the place of residence of the defendant or unknown occupant is stated in any affidavit on file, shall at the same time mail one copy of the notice addressed to such defendant or unknown occupant at such place of residence shown in such affidavit. On or before the day set for the appearance, the sheriff shall file the notice with an endorsement thereon stating the time when and places where the sheriff posted and to whom and at what address he or she mailed copies as required by this Section. For want of sufficient notice any cause may be continued from time to time until the court has jurisdiction of the defendant or unknown occupant.
735 ILCS 5/9-107