55 ILCS 5/3-14020
The head of the institution, department or office in which a position classified under this Division is to be filled, shall notify the president of the board and said commission of that fact, and said commission shall certify to the appointing officer the name and address of the candidate standing highest upon the register for the class or grade said position belongs to, except that in case of laborers, where a choice by competition is impracticable, said commission may provide by its rules that the selection may be made by lot from among those candidates proved fit by examination. In making such certification, sex shall be disregarded. Said appointing officer, meaning thereby the president of said board, shall notify said commission of each position to be filled separately, and shall fill such place by the appointment of the person certified by said commission therefor, which appointment shall be on probation for a period to be fixed by said rules. At or before the expiration of the period of probation, the officer having the power of appointment may, with the consent of said commission, discharge such person so appointed on probation, upon assigning in writing to said commission his or her reasons therefor.
55 ILCS 5/3-14020