MLA
Godfrey, Ervin. Letter from Ervin Godfrey to His Wife. Godfrey Was a Doctor from Madison, Georgia - April 12, 1861. 1861. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 3, Folder 37. https://digital.library.emory.edu/purl/368kd51d5s-cor.
APA, 6th edition
Godfrey, E. (1861). Letter from Ervin Godfrey to his wife. Godfrey was a doctor from Madison, Georgia - April 12, 1861 (Box 3, Folder 37) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/368kd51d5s-cor.
Chicago
Godfrey, Ervin. “Letter from Ervin Godfrey to His Wife. Godfrey Was a Doctor from Madison, Georgia - April 12, 1861.” Letters (correspondence). Civil War Collection, 1861. Box 3, Folder 37. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/368kd51d5s-cor.