MLA
Tillinghast, Thomas F. Letter from Thomas F. Tillinghast (Camp Jackson) to His Sister, Cornelia E. Tillinghast (Gillisonville, South Carolina). Thomas Served in the 3rd South Carolina Cavalry - April 16, 1864. 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 6, Folder 55. https://digital.library.emory.edu/purl/699n2z35j8-cor.
APA, 6th edition
Tillinghast, T. F. (1864). Letter from Thomas F. Tillinghast (Camp Jackson) to his sister, Cornelia E. Tillinghast (Gillisonville, South Carolina). Thomas served in the 3rd South Carolina Cavalry - April 16, 1864 (Box 6, Folder 55) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/699n2z35j8-cor.
Chicago
Tillinghast, Thomas F. “Letter from Thomas F. Tillinghast (Camp Jackson) to His Sister, Cornelia E. Tillinghast (Gillisonville, South Carolina). Thomas Served in the 3rd South Carolina Cavalry - April 16, 1864.” Letters (correspondence). Civil War Collection, 1864. Box 6, Folder 55. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/699n2z35j8-cor.