MLA

Mason, William Smith, 1866-. Thomas Jefferson: letter to Judge James Semple; also Judge Semple's reply; Monticello. Box 28, folder 1972. 1812 October 2. https://collections.library.yale.edu/catalog/2033572.

APA, 6th edition

Mason, William Smith, 1866-. (["Box 28, folder 1972"])(1812 October 2)[Thomas Jefferson: letter to Judge James Semple; also Judge Semple's reply; Monticello]. https://collections.library.yale.edu/catalog/2033572.