70 ILCS 1215/9
From the return or report of examiners or from the examinations made by the Civil Service Board the secretary of the Civil Service Board shall prepare a register for each grade or class of position in the classified service of the Park Employees' and Retirement Board Employees' Annuity and Benefit Fund of the persons who shall attain such minimum mark as may be fixed by the Civil Service Board for any part of such examination, and whose general average standing upon examination for such grade or class is not less than the minimum fixed by the rules of said Board, and who are otherwise eligible; and such persons shall take rank upon the register as candidates in the order of their relative excellence as determined by examination, without reference to priority of time of examination.
Said Board may in its discretion cancel such portion of any such register as has been in force for more than two (2) years.
70 ILCS 1215/9