Here's a very helpful online guide from University of Illinois Library website:
This guide describes effective search techniques for locating primary sources in catalogs, indexes, and online archives.
Note that many of the reference resources, citation index collections and online primary resource archives listed on this guide are also available through the KSL website.
Also be aware that there are other physical and electronic collections in the Case Libraries system that provide lots of primary sources. Locations for these resources are indicated in Case Libraries online catalog records.
KSL hosts several collections of major American newspapers in full text, spanning the 19th and 20th centuries.
The Readers' Guide is a key research resource for exploring 20th century American history and popular culture as chronicled in mainstream periodicals. KSL has a print copy of this multi-volume index on the first floor of the library.