MLA
Lewis, James. Letter from James Lewis (Centerville, Virginia) to "Dear Friend" - October 10, 1861. 1861. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 4, Folder 44. https://digital.library.emory.edu/purl/218dfn3065-cor.
APA, 6th edition
Lewis, J. (1861). Letter from James Lewis (Centerville, Virginia) to "Dear Friend" - October 10, 1861 (Box 4, Folder 44) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/218dfn3065-cor.
Chicago
Lewis, James. “Letter from James Lewis (Centerville, Virginia) to ‘Dear Friend’ - October 10, 1861.” Letters (correspondence). Civil War Collection, 1861. Box 4, Folder 44. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/218dfn3065-cor.