Each university of the University of Illinois System follows a different academic calendar, which means that important dates and deadlines (such as the first and last day of classes, last day to drop a class, etc.) vary from university to university. In addition, some online courses (e.g., NetMath courses from Urbana) are self-paced and do not follow a strict calendar.
Pay close attention to the calendar for your homeuniversity and your course or program information to be sure that you are aware of the dates and deadlines that affect you.
Academic calendars by university can be found by following the links below.
Urbana-Champaign - https://registrar.illinois.edu/academic-calendars/
Chicago - https://catalog.uic.edu/ucat/
Springfield - https://www.uis.edu/registration/calendars/