[some elements should be dropped, if they are not available]:
Author (last name, first). Title or description of document (date). Collection name. Collection/item number. [Name of] Special Collections and Archives, Link to webpage(s), if applicable.
Sample Citation:
Sanford Cobb, Letter to James Jackson, 6 July 1960, Sanford (Sandy) Cobb Papers, 1955-1998, Letters, Box 1, Folder 1. Watkinson Library, Trinity College, Hartford, CT.