Henry Fonda was generally unhappy with the quality of the films he had to do while under contract to 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.
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 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.
William A. Wellman had wanted to adapt the novel for the screen for years and he harangued Darryl F. Zanuck until the mogul finally caved in. Wellman pointed out that he had successfully delivered social messages in the past, in such well-received films as The Public Enemy (1931) and A Star Is Born (1937). But Zanuck was concerned that the American public wasn't ready for a film that centered on lynching. Zanuck relented when Wellman happily agreed that he would also direct two far-less adventurous pictures for the producer- Thunder Birds: Soldiers of the Air (1942) and Buffalo Bill (1944).
William A. Wellman had discussed making the film in 1940, with producer Harold Hurley. But Hurley had a completely different sort of film in mind, one that would revolve around Mae West as a saloon hostess! When Hurley left Paramount, he sold Ox-bow's rights to Wellman for $6,500. "I bought the property from Harold Hurley," he later said, "after he had gotten into some sort of beef with the big boys and was relieved of his job...then I went to all the producers for whom I had worked and got turned down. Zanuck was the only one with the guts to do an out-of-the-ordinary story for the prestige, rather than the dough."
The trivia items below may give away important plot points.
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 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.