65 ILCS 5/5-2-1
If a city or village adopts the managerial form of municipal government and also elects to choose alderpersons or trustees, as the case may be, from wards or districts, then the city council shall be constituted as provided in Sections 5-2-2 through 5-2-10 and the village board shall be constituted as provided in Section 5-2-11 and the incumbent alderpersons , trustees, mayor, president, clerk and treasurer shall continue in office until expiration of their present terms. If a city has voted to elect only one alderperson from each ward then no election for a successor for the alderperson from each ward whose term next expires shall be held, and upon the expiration of the terms of the alderpersons having the longest time to serve at the time of adoption of this Article 5 only one successor shall be elected from each ward. In case a city votes to elect only one alderperson from each ward, the number of alderpersons prescribed by Section 5-2-2 shall be halved, for the purposes of this Article 5 and the provisions of Section 5-2-4 prescribing the number of wards shall not apply but such city shall have an equal number of wards and alderpersons . The mayor of a city and the president of a village board shall be elected from the city or village at large.
65 ILCS 5/5-2-1