MLA
Harrison, John W. Letter from John W. Harrison (Camp near Frederick, Maryland) to "Dear Mother" - September 9, 1862. 1862. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 3, Folder 53. https://digital.library.emory.edu/purl/40644j10nx-cor.
APA, 6th edition
Harrison, J. W. (1862). Letter from John W. Harrison (camp near Frederick, Maryland) to "Dear Mother" - September 9, 1862 (Box 3, Folder 53) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/40644j10nx-cor.
Chicago
Harrison, John W. “Letter from John W. Harrison (Camp near Frederick, Maryland) to ‘Dear Mother’ - September 9, 1862.” Letters (correspondence). Civil War Collection, 1862. Box 3, Folder 53. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/40644j10nx-cor.