MLA
Walcott, Charles F. (Charles Folsom). History of the Twenty-first Regiment, Massachusetts Volunteers, in the war for the preservation of the Union, 1861-1865 : with statistics of the war and of rebel prisons. 1882. Regimental Histories. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/39995x6fs2-cor.
APA, 6th edition
Walcott, Charles F. (Charles Folsom). (1882)[History of the Twenty-first Regiment, Massachusetts Volunteers, in the war for the preservation of the Union, 1861-1865 : with statistics of the war and of rebel prisons]. Regimental Histories, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/39995x6fs2-cor.
Chicago
Walcott, Charles F. (Charles Folsom), History of the Twenty-first Regiment, Massachusetts Volunteers, in the war for the preservation of the Union, 1861-1865 : with statistics of the war and of rebel prisons, 1882, Regimental Histories, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/39995x6fs2-cor.