MLA

Cooper, James Fenimore, 1789-1851. Pomeroy, Ann Cooper. Box 13, folder 346. circa 1833. https://collections.library.yale.edu/catalog/17073661.

APA, 6th edition

Cooper, James Fenimore, 1789-1851. (["Box 13, folder 346"])(circa 1833)[Pomeroy, Ann Cooper]. https://collections.library.yale.edu/catalog/17073661.