MLA
McCue, C. A. Letter from C. A. McCue (Glasgow, Kentucky) to "Dear Elizabeth." McCue Served in the 37th Kentucky Mounted Infantry, Company C - September 16, 1863. 1863. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 5, Folder 3. https://digital.library.emory.edu/purl/873pvmcwgw-cor.
APA, 6th edition
McCue, C. A. (1863). Letter from C. A. McCue (Glasgow, Kentucky) to "Dear Elizabeth." McCue served in the 37th Kentucky Mounted Infantry, Company C - September 16, 1863 (Box 5, Folder 3) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/873pvmcwgw-cor.
Chicago
McCue, C. A. “Letter from C. A. McCue (Glasgow, Kentucky) to ‘Dear Elizabeth." McCue Served in the 37th Kentucky Mounted Infantry, Company C - September 16, 1863.” Letters (correspondence). Civil War Collection, 1863. Box 5, Folder 3. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/873pvmcwgw-cor.