MLA
McGaughey, John T. B. Letter from John T. B. McGaughey (Verona, Mississippi) to "Dear Cousin" - January 11, 1865. 1865. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 5, Folder 4. https://digital.library.emory.edu/purl/136h18943g-cor.
APA, 6th edition
McGaughey, J. T. B. (1865). Letter from John T. B. McGaughey (Verona, Mississippi) to "Dear Cousin" - January 11, 1865 (Box 5, Folder 4) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/136h18943g-cor.
Chicago
McGaughey, John T. B. “Letter from John T. B. McGaughey (Verona, Mississippi) to ‘Dear Cousin’ - January 11, 1865.” Letters (correspondence). Civil War Collection, 1865. Box 5, Folder 4. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/136h18943g-cor.