MLA
Tillinghast, Edwin L. Letter from Edwin L. Tillinghast (near Yorktown, Virginia) to His Sister, Cornelia E. Tillinghast (Gillisonville, South Carolina). Edwin Served in the 3rd South Carolina Cavalry - April 30, 1862. 1862. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 6, Folder 55. https://digital.library.emory.edu/purl/648ffbg816-cor.
APA, 6th edition
Tillinghast, E. L. (1862). Letter from Edwin L. Tillinghast (near Yorktown, Virginia) to his sister, Cornelia E. Tillinghast (Gillisonville, South Carolina). Edwin served in the 3rd South Carolina Cavalry - April 30, 1862 (Box 6, Folder 55) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/648ffbg816-cor.
Chicago
Tillinghast, Edwin L. “Letter from Edwin L. Tillinghast (near Yorktown, Virginia) to His Sister, Cornelia E. Tillinghast (Gillisonville, South Carolina). Edwin Served in the 3rd South Carolina Cavalry - April 30, 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/648ffbg816-cor.