735 ILCS 5/2-202
§ 2-202. Persons authorized to serve process; Place of service; Failure to make return.
(a) Process shall be served by a sheriff, or if the sheriff is disqualified, by a coroner of some county of the State. A sheriff of a county with a population of less than 1,000,000 may employ civilian personnel to serve process. In counties with a population of less than 1,000,000, process may be served, without special appointment, by a person who is licensed or registered as a private detective . . . . The court may, in its discretion upon motion, order service to be made by a private person over 18 years of age and not a party to the action. It is not necessary that service be made by a sheriff or coroner of the county in which service is made. If served or sought to be served by a sheriff or coroner, he or she shall endorse his or her return thereon, and if by a private person the return shall be by affidavit.
(b) Summons may be served upon the defendants wherever they may be found in the State, by any person authorized to serve process. . . .
* * *
735 ILCS 5/2-203
§ 2-203. Service on individuals.
(a) Except as otherwise expressly provided, service of summons upon an individual defendant shall be made (1) by leaving a copy of the summons with the defendant personally, (2) by leaving a copy at the defendant's usual place of abode, with some person of the family or a person residing there, of the age of 13 years or upwards, and informing that person of the contents of the summons, provided the officer or other person making service shall also send a copy of the summons in a sealed envelope with postage fully prepaid, addressed to the defendant at his or her usual place of abode . . . .
(b) The officer, in his or her certificate or in a record filed and maintained in the Sheriff's office, or other person making service, in his or her affidavit or in a record filed and maintained in his or her employer's office, shall (1) identify as to sex, race, and approximate age the defendant or other person with whom the summons was left and (2) state the place where (whenever possible in terms of an exact street address) and the date and time of the day when the summons was left with the defendant or other person.