MLA
Martin, A. M. Letter from A. M. Martin (Sedalia, Missouri) to "Dear Coz;" Martin Discusses Life in Missouri during the War and the Freed Men and Women There - September 27, 1864 (Typescript). 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 19, Folder 46. https://digital.library.emory.edu/purl/883xsj3w36-cor.
APA, 6th edition
Martin, A. M. (1864). Letter from A. M. Martin (Sedalia, Missouri) to "Dear Coz;" Martin discusses life in Missouri during the war and the freed men and women there - September 27, 1864 (typescript) (Box 19, Folder 46) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/883xsj3w36-cor.
Chicago
Martin, A. M. “Letter from A. M. Martin (Sedalia, Missouri) to ‘Dear Coz;" Martin Discusses Life in Missouri during the War and the Freed Men and Women There - September 27, 1864 (Typescript).” Letters (correspondence). Civil War Collection, 1864. Box 19, Folder 46. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/883xsj3w36-cor.