65 ILCS 5/5-2-18
In any city which has adopted this Article 5 and which elects a mayor and councilmen as provided in Section 5-2-12, a proposition to elect alderpersons from wards as provided in Article 3 of this Code, except that only one alderperson may be elected from each ward, shall be certified by the city clerk to the proper election authority who shall submit such proposition at the general municipal election in accordance with the general election law, if a petition signed by electors of the city numbering not less than 10% of the total vote cast for mayor at the last preceding election, is filed with the city clerk.
The proposition shall be substantially in the following form:
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Shall the city of.... be divided into wards with one alderperson to be elected from each ward, but with the ------- | YES ------------- |
mayor to be elected from the city NO at large? |
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If a majority of those voting on the proposition vote "yes", then the sitting city council shall proceed to divide the city into wards in the manner provided in Article 3 and one alderperson shall be elected from each ward at the next general municipal election of any city officer. Upon the election and qualification of such alderpersons the terms of office of all sitting councilmen shall expire. After the adoption of such proposition the provisions of Article 3 shall be applicable to the division of the city into wards and to the election of the mayor and alderpersons of such city, except that only one alderperson shall be elected from each ward.
65 ILCS 5/5-2-18