MLA

Carlingford, Theobald Taaffe, Earl of, -1677. ALS, Brussels. Box 1, folder 17. [1658] Jun 23. https://collections.library.yale.edu/catalog/15298740.

APA, 6th edition

Carlingford, Theobald Taaffe, Earl of, -1677. (["Box 1, folder 17"])([1658] Jun 23)[ALS, Brussels]. https://collections.library.yale.edu/catalog/15298740.