MLA

Whitman, Walt, 1819-1892. Whitman family. Box 2, folder 89. 1875. https://collections.library.yale.edu/catalog/2053723.

APA, 6th edition

Whitman, Walt, 1819-1892. (["Box 2, folder 89"])(1875)[Whitman family]. https://collections.library.yale.edu/catalog/2053723.