735 ILCS 5/12-813
A judgment by confession without service of process on the defendant shall not be the basis for seeking a deduction order, unless such judgment is confirmed after service of process by a trial de novo, as if such confession of judgment had not been obtained, except that if it appears by the return of the officer on the first summons that the employee is not found, alias summonses subsequently issued may be served upon the employee by leaving a copy thereof with the employee's employer, or leaving a copy thereof at the usual place of business of the employer with his or her superintendent, manager, cashier, general agent or clerk, pursuant to an affidavit filed by the creditor with the clerk of the court stating the identity of the employee's employer, and that the employee is actively employed at the time such alias is sought, and except that if a notice of defense has been filed to a wage assignment as provided in Section 4.1 of "An Act to promote the welfare of wage earners by regulating the assignment of wages, and prescribing a penalty for the violation thereof", approved July 1, 1935, as amended, the debtor may be served by registered or certified mail within 6 months after the filing of such defense on a wage assignment in the action to confirm the judgment by confession and such mailing by the creditor to the address shown on the notice of defense shall constitute service of the summons.
735 ILCS 5/12-813