MLA
Kent, George W. Letter from George Kent (Jefferson Barracks, Missouri) to "Dear Father and Mother" - December 2, 1863. 1863. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 4, Folder 29. https://digital.library.emory.edu/purl/6214mw6n9p-cor.
APA, 6th edition
Kent, G. W. (1863). Letter from George Kent (Jefferson Barracks, Missouri) to "Dear Father and Mother" - December 2, 1863 (Box 4, Folder 29) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/6214mw6n9p-cor.
Chicago
Kent, George W. “Letter from George Kent (Jefferson Barracks, Missouri) to ‘Dear Father and Mother’ - December 2, 1863.” Letters (correspondence). Civil War Collection, 1863. Box 4, Folder 29. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/6214mw6n9p-cor.