Henry Fonda was generally unhappy with the quality of the films he had to do while under contract with 20th Century Fox. This was one of only two films from that period that he was actually enthusiastic about starring in. The other was The Grapes of Wrath (1940).
Director William A. Wellman loved the novel "The Ox-Bow Incident" and had long wanted to make it into a film, but the rights-holders insisted that he cast Mae West in any adaptation, which Wellman thought was ridiculous. Finally, Wellman bought the rights himself, and proceeded to make the film "his" way.
The Hays Office--the industry's censors--initially was reluctant to approve the script because of its suggestion that the sheriff condoned the lynchings. The treatment of the lynchings and the characterization of those participating were discussed by the PCA and the studio at great length, and in a June 9, 1942 letter, PCA director Joseph Breen advised studio public relations head Jason S. Joy that the script would be approved if: "Major Tetley's" suicide is retained, "thus constituting a punishment for the ring-leader of the lynching party;" there is an indication that the whole gang will be arrested; the character of "Gil" is rewritten to make him less callous and more active in trying to stop the lynchings; and "Davies'" denunciation of the killings is retained.
The production on the film would be shut down for a week or ten days "due to the $5,000-per-film limit on new construction materials." During the shutdown, already used sets were torn down so that their material could be re-used to build the mountain pass set. Studio publicity noted that the Ox-Bow Valley setting was "the largest set ever constructed" by Fox, and that it covered 26,703 feet.
Sara Allgood was originally cast in the role of "Jennie 'Ma' Grier," but was replaced by Florence Bates. Bates was then injured in a horseback riding scene, necessitating her replacement by Jane Darwell, who appears in the finished film.
The trivia items below may give away important plot points.
The early versions of the script included the suicide of "Gerald Tetley" and that the film was to end with the reappearance of "Rose Mapen" and her husband in the saloon rather than with "Gil" and "Art" leaving to take the letter to "Martin's" wife. The contents of Martin's letter are not revealed in the book, but director William A. Wellman thought that it was important to make them explicit and had Lamar Trotti compose the letter.