The cantankerous Walter Brennan disliked John Ford so much that he never worked with him again. One time when Brennan was having trouble getting into the saddle, Ford yelled, "Can't you even mount a horse?" Brennan shot back, "No, but I got three Oscars for acting!"
John Ford was asked by a film historian why he changed the historical details of the famous gunfight if, as he claimed, the real Wyatt Earp had told him all about it on a movie set back in the 1920s. "Did you like the film?" Ford asked, to which the scholar replied it was one of his favorites. "What more do you want?" Ford snapped.
Walter Brennan, John Ireland, and Grant Withers were required to do their own riding and shooting in the scene where the clan rides into town during a dust storm. John Ford used a powerful wind machine and told the actors to fire their guns close to the horses' ears to make them ride wild.
John Ford, who in his youth had known the real Wyatt Earp, claimed the way the OK Corral gunfight was staged in this film was the way it was explained to him by Earp himself, with a few exceptions. Ford met Earp through Harry Carey.
John Ford wanted to shoot in Monument Valley, UT, which had proven to be the perfect site for Stagecoach (1939) and would quickly become his favorite location and the landscape most closely associated with his vision of the Old West. The real town of Tombstone, AZ, however, lies at the southern end of the state, closer to the Arizona-Mexico border. So he had a set for the complete town built at a cost of $250,000. Ford also chose Monument Valley because he wanted to bring some business to the economically depressed Navajo community there.