MLA
Boykin, Key L. Letter from Key L. Boykin (Humboldt, Tennessee) to [Unknown Recipient] - June 16, 1878. 1878. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 6, Folder 44. https://digital.library.emory.edu/purl/675r7sqw1w-cor.
APA, 6th edition
Boykin, K. L. (1878). Letter from Key L. Boykin (Humboldt, Tennessee) to [unknown recipient] - June 16, 1878 (Box 6, Folder 44) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/675r7sqw1w-cor.
Chicago
Boykin, Key L. “Letter from Key L. Boykin (Humboldt, Tennessee) to [Unknown Recipient] - June 16, 1878.” Letters (correspondence). Civil War Collection, 1878. Box 6, Folder 44. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/675r7sqw1w-cor.