Here is an example of the preferred citation style for a collection housed in the Criss Library Archives and Special Collections:
Mary Ellen Williamson Women Airforce Service Pilots (WASP) Collection, Archives and Special Collections, Dr. C.C. and Mabel L. Criss Library, University of Nebraska at Omaha.
Below are some fictionalized examples of how you might cite an individual item from a collection based on different citation styles:
MLA:
Washington, Cornelia. Letter to Mary E. Williamson. 3 February 1943. Mary Ellen Williamson Women Airforce Service Pilots (WASP) Collection, Archives and Special Collections, Dr. C.C. and Mabel L. Criss Library, University of Nebraska at Omaha.
Chicago:
Cornelia Washington to Mary E. Williamson, 3 February 1943, Box 1, Folder 1, Mary Ellen Williamson Women Airforce Service Pilots (WASP) Collection, Archives and Special Collections, Dr. C.C. and Mabel L. Criss Library, University of Nebraska at Omaha.
APA:
Washington, C. (1943, February 3). [Letter to Mary E. Williamson]. Mary Ellen Williamson Women Airforce Service Pilots (WASP) Collection, Archives and Special Collections, Dr. C.C. and Mabel L. Criss Library, University of Nebraska at Omaha.