Each campus of the University of Illinois 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 campus to campus. 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 home campus and your course or program information to be sure that you are aware of the dates and deadlines that affect you.
Academic calendars by campus can be found by following the links below.
Urbana-Champaign - http://registrar.illinois.edu/spring-academic-calendarl
Chicago - http://www.uic.edu/ucat/catalog/CA.shtml
Springfield - http://www.uis.edu/registration/calendars