65 ILCS 5/6-3-5: Division into wards.

Every city shall have as many wards as one-half the total number of alderpersons to which the city is entitled. The city council, from time to time shall divide the city into that number of wards. In the formation of wards the population of each ward as determined by the latest city, state or national census shall be as nearly equal and the wards shall be of as compact and contiguous territory, as practicable.