40 ILCS 5/3-103

"Municipality": (1) Any city, village or incorporated town of 5,000 or more but less than 500,000 inhabitants, as determined from the United States Government statistics or a census taken at any time by the city, village or incorporated town and (2) any city, village or incorporated town of less than 5,000 inhabitants which, by referendum held under Section 3-145 adopts this Article.