MLA
Reep, Sarah A. Letter from Sarah A. Reep (Ohio), Mother of Reuben Reep, to Her Son, Jacob - June 18, 1865. 1865. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 20, Folder 17. https://digital.library.emory.edu/purl/419s1rn9tz-cor.
APA, 6th edition
Reep, S. A. (1865). Letter from Sarah A. Reep (Ohio), mother of Reuben Reep, to her son, Jacob - June 18, 1865 (Box 20, Folder 17) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/419s1rn9tz-cor.
Chicago
Reep, Sarah A. “Letter from Sarah A. Reep (Ohio), Mother of Reuben Reep, to Her Son, Jacob - June 18, 1865.” Letters (correspondence). Civil War Collection, 1865. Box 20, Folder 17. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/419s1rn9tz-cor.