MLA
Godfrey, Ervin. Letter from Ervin Godfrey to His Wife. Godfrey Was a Doctor from Madison, Georgia - January 27, 1868. 1868. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 3, Folder 37. https://digital.library.emory.edu/purl/180vq83chk-cor.
APA, 6th edition
Godfrey, E. (1868). Letter from Ervin Godfrey to his wife. Godfrey was a doctor from Madison, Georgia - January 27, 1868 (Box 3, Folder 37) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/180vq83chk-cor.
Chicago
Godfrey, Ervin. “Letter from Ervin Godfrey to His Wife. Godfrey Was a Doctor from Madison, Georgia - January 27, 1868.” Letters (correspondence). Civil War Collection, 1868. Box 3, Folder 37. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/180vq83chk-cor.