MLA
Griffin, John L. Letter from John L. Griffin (Charlestown, Virginia), to "Dear Sister" - August 23, 1864. 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 3, Folder 41. https://digital.library.emory.edu/purl/566j0zpd8f-cor.
APA, 6th edition
Griffin, J. L. (1864). Letter from John L. Griffin (Charlestown, Virginia), to "Dear Sister" - August 23, 1864 (Box 3, Folder 41) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/566j0zpd8f-cor.
Chicago
Griffin, John L. “Letter from John L. Griffin (Charlestown, Virginia), to ‘Dear Sister’ - August 23, 1864.” Letters (correspondence). Civil War Collection, 1864. Box 3, Folder 41. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/566j0zpd8f-cor.