MLA
Barr, Wolcott S. Letter from Wolcott S. Barr (Falmouth, Virginia) to His Brother, Eugene. Wolcott S. Barr Served in Company I of the New York 80th Volunteer Infantry Regiment. 1862. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 19, Folder 3. https://digital.library.emory.edu/purl/344pk0p3sb-cor.
APA, 6th edition
Barr, W. S. (1862). Letter from Wolcott S. Barr (Falmouth, Virginia) to his brother, Eugene. Wolcott S. Barr served in Company I of the New York 80th Volunteer Infantry Regiment (Box 19, Folder 3) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/344pk0p3sb-cor.
Chicago
Barr, Wolcott S. “Letter from Wolcott S. Barr (Falmouth, Virginia) to His Brother, Eugene. Wolcott S. Barr Served in Company I of the New York 80th Volunteer Infantry Regiment.” Letters (correspondence). Civil War Collection, 1862. Box 19, Folder 3. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/344pk0p3sb-cor.