MLA
McKinney, Chris C. Envelope Containng Letter from Christ C. McKinney to His Wife, Mary (Petersburg, Tennessee). McKinney Served in the 8th Tennessee Infantry Regiment - January 21, 1862. 1862. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 5, Folder 7. https://digital.library.emory.edu/purl/9182jm650d-cor.
APA, 6th edition
McKinney, C. C. (1862). Envelope containng letter from Christ C. McKinney to his wife, Mary (Petersburg, Tennessee). McKinney served in the 8th Tennessee Infantry Regiment - January 21, 1862 (Box 5, Folder 7) [Envelopes]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/9182jm650d-cor.
Chicago
McKinney, Chris C. “Envelope Containng Letter from Christ C. McKinney to His Wife, Mary (Petersburg, Tennessee). McKinney Served in the 8th Tennessee Infantry Regiment - January 21, 1862.” Envelopes. Civil War Collection, 1862. Box 5, Folder 7. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/9182jm650d-cor.