MLA

Backus, Isaac, 1724-1806. Church records: Connecticut. Box 6, folder 5. Undated. https://collections.library.yale.edu/catalog/33553793.

APA, 6th edition

Backus, Isaac, 1724-1806. (["Box 6, folder 5"])(Undated)[Church records: Connecticut]. https://collections.library.yale.edu/catalog/33553793.