65 ILCS 20/21-38: Redistricting every ten years.

If the city council has not redistricted the City of Chicago since the taking of the national census of 1940, then within three months after the adoption of this Article by the voters it shall be the duty of the city council to pass an ordinance redistricting the city into fifty wards in accordance with the provisions of this Article.

On or before the first day of December, of the year following the year in which the national census is taken, and every ten years thereafter, the city council shall by ordinance redistrict the city on the basis of the national census of the preceding year. All elections of alderpersons shall be held from the existing wards until a redistricting is had as provided for in this Article.