MLA
Hofflinger, Erastus. Letter from Erastus Hofflinger (near Whight Oak Church, Virginia) to His Sister. Hofflinger Was a Member of the 23rd New Jersey Infantry Regiment, Company D - April 6, 1863. 1863. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 19, Folder 36. https://digital.library.emory.edu/purl/269m37pwsn-cor.
APA, 6th edition
Hofflinger, E. (1863). Letter from Erastus Hofflinger (near Whight Oak Church, Virginia) to his sister. Hofflinger was a member of the 23rd New Jersey Infantry Regiment, Company D - April 6, 1863 (Box 19, Folder 36) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/269m37pwsn-cor.
Chicago
Hofflinger, Erastus. “Letter from Erastus Hofflinger (near Whight Oak Church, Virginia) to His Sister. Hofflinger Was a Member of the 23rd New Jersey Infantry Regiment, Company D - April 6, 1863.” Letters (correspondence). Civil War Collection, 1863. Box 19, Folder 36. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/269m37pwsn-cor.