These sources may be good starting places. The cannot be checked out, and are found in the Reference Collection on the 1st floor of the UI Library.
American Folklore by 
Funk & Wagnalls standard dictionary of folklore, mythology and legend by 
The Greenwood Encyclopedia of Folktales and Fairy Tales by 
The Greenwood Encyclopedia of World Folklore and Folklife by ![University of Idaho Library [logo]](https://www.lib.uidaho.edu/media/images/ui_library_horizontal.png)