65 ILCS 5/10-1-3
The commissioners shall classify all the offices and places of employment in such municipality with reference to the examinations hereinafter provided for, except those offices and places excluded by Section 10-1-17. The offices and places so classified by the commission shall constitute the classified civil service of such municipality. No appointments to any of such offices or places shall be made except under and according to the rules hereinafter mentioned.
The commissioners shall also classify all positions of employment in respect to employees whose employment is transferred to the municipality by virtue of "An Act in relation to the exchange of certain functions, property and personnel among cities, and park districts having coextensive geographic areas and populations in excess of 500,000," approved July 5, 1957, as heretofore and hereafter amended, and such positions of employment shall be included in the classified civil service of the municipality.
65 ILCS 5/10-1-3