MLA
Wheeler, Dan, Jr. Letter from Dan Jr. Wheeler (Camp near New Market, Virginia) to "Dear Willie" - November 15, 1864. 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 7, Folder 20. https://digital.library.emory.edu/purl/747dr7srwx-cor.
APA, 6th edition
Wheeler, D., Jr. (1864). Letter from Dan Jr. Wheeler (Camp near New Market, Virginia) to "Dear Willie" - November 15, 1864 (Box 7, Folder 20) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/747dr7srwx-cor.
Chicago
Wheeler, Dan, Jr. “Letter from Dan Jr. Wheeler (Camp near New Market, Virginia) to ‘Dear Willie’ - November 15, 1864.” Letters (correspondence). Civil War Collection, 1864. Box 7, Folder 20. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/747dr7srwx-cor.