MLA

Buck, Daniel Webster, 1840-1892. 8th Illinois Cavalry Regiment letter, Chicago, Illinois, to Galena and Chicago Union Railroad. Box 1, folder 20. 1864 February 23. https://collections.library.yale.edu/catalog/17437198.

APA, 6th edition

Buck, Daniel Webster, 1840-1892. (["Box 1, folder 20"])(1864 February 23)[8th Illinois Cavalry Regiment letter, Chicago, Illinois, to Galena and Chicago Union Railroad]. https://collections.library.yale.edu/catalog/17437198.