735 ILCS 5/2-203.2
For the security of a correctional institution or facility or jail, a process server may be refused entry into that correctional institution or facility or jail. Each correctional institution or facility or jail shall designate a representative to accept service from a licensed or registered private detective or agency for purposes of effectuating service upon an inmate in the custody of the institution, facility, or jail. With respect to an inmate incarcerated in an Illinois Department of Corrections facility, the process server shall contact the chief administrative officer in advance to arrange and designate the time and date, during regularly scheduled business hours, that the facility representative will meet with and accept service from the process server. Service upon a warden's or sheriff's representative shall constitute substitute service and a mailing to the inmate of the process shall be completed by the server in accordance with Section 2-202. A warden's or sheriff's representative accepting substitute service shall forward the process to the inmate, but if for any reason the process is not forwarded to the inmate, the sheriff, sheriff's representative, warden, or warden's representative shall not be responsible for any civil fine or penalty, or have other liability. If for any reason an inmate is not in the correctional institution or facility or jail at the time of the service of process, a warden's or sheriff's representative may refuse to accept service for the inmate. If it is determined after the process has been left with the designated representative, that the inmate is not present at that institution or facility or jail, the designated representative shall promptly return it to the licensed or registered private detective or agency, indicating that the substitute service could not be effectuated. The process server shall promptly notify the court of the unsuccessful service.
735 ILCS 5/2-203.2