From the Illinois Municipal League’s web site:
Pursuant to Illinois law, municipal officials are required to perform certain duties at specified times throughout the calendar year. The IML has compiled those duties as a service to their members, and we thank them.
Non-home rule municipal officials must always comply with these statutory requirements. Home rule municipalities, however, must only comply with the requirements set forth by the statutes until such time as they may otherwise provide by ordinance, unless the power has been preempted by statute. Some requirements are set according to the calendar year, while others are set according to the fiscal year. Read more.