The University of Illinois almost always takes its allowed five business days to respond to a Freedom of Information Request and frequently asks for an extension of five days because of the sheer amount of volume of Freedom of Information requests.
If you are looking for information about a specific campus or the university as a whole, it is useful to make that clear in your request.
A great deal of information about the university is kept on websites available to the public, so they are often worth checking out before you file a request. The Division of Management Information website keeps information about enrollment figures, admissions information and faculty and staff size, among other information.
The University of Illinois keeps an online FOIA Log. This is not an exhaustive list of all requests, but it is useful for seeing what type of information is requested.