MLA
Simmons, W. C. Letter from W. C. Simmons (Yorktown, Virginia) to Lemuel Dudley (Madison County, Georgia) - February 12, 1862. 1862. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 6, Folder 22. https://digital.library.emory.edu/purl/3720cfxqbw-cor.
APA, 6th edition
Simmons, W. C. (1862). Letter from W. C. Simmons (Yorktown, Virginia) to Lemuel Dudley (Madison County, Georgia) - February 12, 1862 (Box 6, Folder 22) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/3720cfxqbw-cor.
Chicago
Simmons, W. C. “Letter from W. C. Simmons (Yorktown, Virginia) to Lemuel Dudley (Madison County, Georgia) - February 12, 1862.” Letters (correspondence). Civil War Collection, 1862. Box 6, Folder 22. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/3720cfxqbw-cor.