MLA
Cook, James Walter. Letter from James Walker Cook (near Maryville, Tennessee) to His Wife Sue (Prairie Bluff, Alabama). Cook Was a Private in Company C of the 3rd Alabama Cavalry - February 22, 1864. 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 2, Folder 34. https://digital.library.emory.edu/purl/969866t2jk-cor.
APA, 6th edition
Cook, J. W. (1864). Letter from James Walker Cook (near Maryville, Tennessee) to his wife Sue (Prairie Bluff, Alabama). Cook was a private in Company C of the 3rd Alabama Cavalry - February 22, 1864 (Box 2, Folder 34) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/969866t2jk-cor.
Chicago
Cook, James Walter. “Letter from James Walker Cook (near Maryville, Tennessee) to His Wife Sue (Prairie Bluff, Alabama). Cook Was a Private in Company C of the 3rd Alabama Cavalry - February 22, 1864.” Letters (correspondence). Civil War Collection, 1864. Box 2, Folder 34. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/969866t2jk-cor.