MLA
Willard, Levi. Letter from Levi Willard (Springfield, Ohio) to Milton A. Candler, Responding to Inaccuracies in Jacob D. Cox's History of the Atlanta Campaign - August 31, 1882. 1882. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 9, Folder 47. https://digital.library.emory.edu/purl/808v9s4nzr-cor.
APA, 6th edition
Willard, L. (1882). Letter from Levi Willard (Springfield, Ohio) to Milton A. Candler, responding to inaccuracies in Jacob D. Cox's history of the Atlanta Campaign - August 31, 1882 (Box 9, Folder 47) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/808v9s4nzr-cor.
Chicago
Willard, Levi. “Letter from Levi Willard (Springfield, Ohio) to Milton A. Candler, Responding to Inaccuracies in Jacob D. Cox's History of the Atlanta Campaign - August 31, 1882.” Letters (correspondence). Civil War Collection, 1882. Box 9, Folder 47. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/808v9s4nzr-cor.