MLA
Rogers, John. Letter from John Rogers (Orange County Courthouse, Virginia) to "Dear Brother." Rogers Served in Company E of the 12th Alabama Infantry Regiment - August 20, 1863. 1863. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 6, Folder 3. https://digital.library.emory.edu/purl/201bk3jb8k-cor.
APA, 6th edition
Rogers, J. (1863). Letter from John Rogers (Orange County Courthouse, Virginia) to "Dear Brother." Rogers served in Company E of the 12th Alabama Infantry Regiment - August 20, 1863 (Box 6, Folder 3) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/201bk3jb8k-cor.
Chicago
Rogers, John. “Letter from John Rogers (Orange County Courthouse, Virginia) to ‘Dear Brother." Rogers Served in Company E of the 12th Alabama Infantry Regiment - August 20, 1863.” Letters (correspondence). Civil War Collection, 1863. Box 6, Folder 3. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/201bk3jb8k-cor.