MLA
O'Kelly, F. C. Letter from F. C. O'Kelly (Epson Spring, Tennessee) to Captain Thomas Maguire - July 19, 1862 (Typescript). 1862. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 7, Folder 15. https://digital.library.emory.edu/purl/4644qrfk82-cor.
APA, 6th edition
O'Kelly, F. C. (1862). Letter from F. C. O'Kelly (Epson Spring, Tennessee) to Captain Thomas Maguire - July 19, 1862 (typescript) (Box 7, Folder 15) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/4644qrfk82-cor.
Chicago
O'Kelly, F. C. “Letter from F. C. O'Kelly (Epson Spring, Tennessee) to Captain Thomas Maguire - July 19, 1862 (Typescript).” Letters (correspondence). Civil War Collection, 1862. Box 7, Folder 15. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/4644qrfk82-cor.