There are several useful books series covering various topics in American Literature.
Search the library catalog for "cambridge companion to" or "oxford companion to" [title keyword search] to find a list of books from these reference series.
Overviews familiarize you with the characters, setting, literary elements, and genre of the work. Overviews can be helpful and informative, but they are not criticism.
You can find overviews at Spark Notes and in a database called Magill On Literature. See Finding Articles for instructions.
NOTE: With few exceptions, overviews and reference books are tertiary sources and should not appear in your Works Cited.