You'll find a wealth of source material on the Internet, often in digital collections from libraries, archives, museums, and government organizations. The trick is how to find them. Google is an option, but you might also consider trying directories and catalogs that specialize in scholarly resources. We recommend the folliwng:
Below are a few examples of the kind of material you can find online.
The UIUC Library also has some unpublished primary source material (archives and manuscripts), but this is a relatively small body of material compared to the abundance of published primary sources held by the Library. Most of the unpublished primary source material will be found in the University Archives, located in the basement of the Main Library, the Student Life and Culture Archive, located east of the President’s house on Florida Avenue in Urbana (1707 S. Orchard St.), and the Illinois Historical Survey (422 Library, moving in September 2009 to 3rd floor of Library). More information is available about the holdings of the University Archives and the Student Life and Culture Archive at their web site (http://www.library.uiuc.edu/ahx), and the archivists can help you identify material on your topic.