65 ILCS 5/3.1-15-5

In all cities incorporated under this Code there shall be elected a mayor, alderpersons, a city clerk, and a city treasurer (except in the case of a city of 10,000 or fewer inhabitants that, by ordinance, allows for the appointment of a city treasurer by the mayor, subject to the advice and consent of the city council). In all villages and incorporated towns, there shall be elected a president, trustees, and a clerk, except as otherwise provided in this Code.