MLA
Johnson, D. G. Letter from D. G. Johnson (Richmond, Virginia) to "Dear Ma and Pa." Johnson Served in Cobb's Brigade, 15th North Carolina Infantry Regiment - June 19, 1862. 1862. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 4, Folder 13. https://digital.library.emory.edu/purl/593ttdz192-cor.
APA, 6th edition
Johnson, D. G. (1862). Letter from D. G. Johnson (Richmond, Virginia) to "Dear Ma and Pa." Johnson served in Cobb's Brigade, 15th North Carolina Infantry Regiment - June 19, 1862 (Box 4, Folder 13) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/593ttdz192-cor.
Chicago
Johnson, D. G. “Letter from D. G. Johnson (Richmond, Virginia) to ‘Dear Ma and Pa." Johnson Served in Cobb's Brigade, 15th North Carolina Infantry Regiment - June 19, 1862.” Letters (correspondence). Civil War Collection, 1862. Box 4, Folder 13. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/593ttdz192-cor.