MLA
Johnson, D. M. Letter from D. M. Johnson (Shelbyville, Tennessee) to "Dear Father" Johnson Served in Company E of the 10th Mississippi Infantry Regiment - January 31, 1863. 1863. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 4, Folder 14. https://digital.library.emory.edu/purl/368kd51d63-cor.
APA, 6th edition
Johnson, D. M. (1863). Letter from D. M. Johnson (Shelbyville, Tennessee) to "Dear Father" Johnson served in Company E of the 10th Mississippi Infantry Regiment - January 31, 1863 (Box 4, Folder 14) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/368kd51d63-cor.
Chicago
Johnson, D. M. “Letter from D. M. Johnson (Shelbyville, Tennessee) to ‘Dear Father’ Johnson Served in Company E of the 10th Mississippi Infantry Regiment - January 31, 1863.” Letters (correspondence). Civil War Collection, 1863. Box 4, Folder 14. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/368kd51d63-cor.