MLA

Kilpatrick, Jack Frederick (1915-1967). Duncan, Walter. Letter to Dollie Duncan on Oklahoma State Penitentiary stationary. Box 22, folder 1842. circa 1950. https://collections.library.yale.edu/catalog/15532646.

APA, 6th edition

Kilpatrick, Jack Frederick (1915-1967). (["Box 22, folder 1842"])(circa 1950)[Duncan, Walter. Letter to Dollie Duncan on Oklahoma State Penitentiary stationary]. https://collections.library.yale.edu/catalog/15532646.