MLA
Crewell, John H. Letters from John H. Crewell (Camp Jackson, Montgomery County, Maryland) to His Father. Crewell Served in the 34th New York Infantry Regiment, Company F - October 14, 1861. 1861. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 19, Folder 16. https://digital.library.emory.edu/purl/81937pvnjp-cor.
APA, 6th edition
Crewell, J. H. (1861). Letters from John H. Crewell (Camp Jackson, Montgomery County, Maryland) to his father. Crewell served in the 34th New York Infantry Regiment, Company F - October 14, 1861 (Box 19, Folder 16) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/81937pvnjp-cor.
Chicago
Crewell, John H. “Letters from John H. Crewell (Camp Jackson, Montgomery County, Maryland) to His Father. Crewell Served in the 34th New York Infantry Regiment, Company F - October 14, 1861.” Letters (correspondence). Civil War Collection, 1861. Box 19, Folder 16. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/81937pvnjp-cor.