MLA
Allen, J. W. Letter from J. W. Allen (Washington, North Carolina) to "Dear Uncle". J. W. Allen Was in Company B of the 24th Georgia Volunteer Infantry Regiment - October 16, 1861. 1861. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 1, Folder 1. https://digital.library.emory.edu/purl/24298sf8mq-cor.
APA, 6th edition
Allen, J. W. (1861). Letter from J. W. Allen (Washington, North Carolina) to "Dear Uncle". J. W. Allen was in Company B of the 24th Georgia Volunteer Infantry Regiment - October 16, 1861 (Box 1, Folder 1) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/24298sf8mq-cor.
Chicago
Allen, J. W. “Letter from J. W. Allen (Washington, North Carolina) to ‘Dear Uncle’. J. W. Allen Was in Company B of the 24th Georgia Volunteer Infantry Regiment - October 16, 1861.” Letters (correspondence). Civil War Collection, 1861. Box 1, Folder 1. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/24298sf8mq-cor.