MLA

Thoreau, Henry David, 1817-1862. Harvard College Library. Box 1, folder 1. 1858 Dec 19. https://collections.library.yale.edu/catalog/2056824.

APA, 6th edition

Thoreau, Henry David, 1817-1862. (["Box 1, folder 1"])(1858 Dec 19)[Harvard College Library]. https://collections.library.yale.edu/catalog/2056824.