MLA

Cooper, James Fenimore, 1789-1851. Cooper, James Fenimore. Box 12, folder 327-333. 1812-1851, undated. https://collections.library.yale.edu/catalog/2055860.

APA, 6th edition

Cooper, James Fenimore, 1789-1851. (["Box 12, folder 327-333"])(1812-1851, undated)[Cooper, James Fenimore]. https://collections.library.yale.edu/catalog/2055860.