MLA
Miller, Robert H. Letter from Robert H. Miller (Richmond, Virginia) to Mary Runa. Miller Served in Company F of the 14th Louisiana Infantry Regiment - November 25, 1861. 1861. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 5, Folder 18. https://digital.library.emory.edu/purl/85370rxxgf-cor.
APA, 6th edition
Miller, R. H. (1861). Letter from Robert H. Miller (Richmond, Virginia) to Mary Runa. Miller served in Company F of the 14th Louisiana Infantry Regiment - November 25, 1861 (Box 5, Folder 18) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/85370rxxgf-cor.
Chicago
Miller, Robert H. “Letter from Robert H. Miller (Richmond, Virginia) to Mary Runa. Miller Served in Company F of the 14th Louisiana Infantry Regiment - November 25, 1861.” Letters (correspondence). Civil War Collection, 1861. Box 5, Folder 18. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/85370rxxgf-cor.