MLA
Tillinghast, Edwin L. Letter from Edwin L. Tillinghast (Manchester Hospital, Virginia) to His Sister, Cornelia E. Tillinghast (Gillisonville, South Carolina). Edwin Served in the 3rd South Carolina Cavalry - September 19, 1862. 1862. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 6, Folder 55. https://digital.library.emory.edu/purl/962f7m0d5r-cor.
APA, 6th edition
Tillinghast, E. L. (1862). Letter from Edwin L. Tillinghast (Manchester Hospital, Virginia) to his sister, Cornelia E. Tillinghast (Gillisonville, South Carolina). Edwin served in the 3rd South Carolina Cavalry - September 19, 1862 (Box 6, Folder 55) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/962f7m0d5r-cor.
Chicago
Tillinghast, Edwin L. “Letter from Edwin L. Tillinghast (Manchester Hospital, Virginia) to His Sister, Cornelia E. Tillinghast (Gillisonville, South Carolina). Edwin Served in the 3rd South Carolina Cavalry - September 19, 1862.” Letters (correspondence). Civil War Collection, 1862. Box 6, Folder 55. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/962f7m0d5r-cor.