John Wayne once remarked that, try as he might, he couldn't get Big John Hamilton to react properly in the scene where McLintock was "explaining" the rules for the fight between Fauntleroy and Dev at the party. Finally, Wayne resorted to actually stomping on Hamilton's foot and kicking him.
Maureen O'Hara wrote in her autobiography that the famous climactic spanking scene was completely authentic and that John Wayne carried it out with such gusto that she had bruises for a week.
When John Wayne needed 500 longhorn steers for a key scene, the Mexican government lent them to him. Mexican longhorns' horns tip up, as opposed to American longhorns, whose horns tip down.
According to producer/son Michael Wayne, in the scene where GW (John Wayne) jumps from a balcony to a pile of hay in a sitting position, Wayne thought it looked like fun and insisted on doing it himself, instead of a stuntman. Although studios frown on a valuable star doing a potentially dangerous stunt, Wayne eventually was allowed to do it, but it was also shot with a stuntman, just in case.
Although often seen as simply a knockabout comedy, John Wayne also intended the film to be a statement of his own political views, his disapproval of the negative representation of Native Americans in previous westerns he had no creative-control over, and his disapproval of wife-beating and marital abuse from either spouse.