MLA
O'Neill, John A., approximately 1836-. Union officer Elmer Ephraim Ellsworth. Ellsworth was the first Union officer to due in the Civil War. 1861?/1880?. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/061djh9x5z-cor.
APA, 6th edition
O'Neill, John A., approximately 1836-. (1861?/1880?)[Union officer Elmer Ephraim Ellsworth. Ellsworth was the first Union officer to due in the Civil War]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/061djh9x5z-cor.
Chicago
O'Neill, John A., approximately 1836-, Union officer Elmer Ephraim Ellsworth. Ellsworth was the first Union officer to due in the Civil War, 1861?/1880?, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/061djh9x5z-cor.