John Wayne was sixty-five years old at the time the movie was filmed. He had already had a cancerous lung removed and was suffering from emphysema. Wayne was so weakened that he had to use a stepladder to climb onto his horse in the film. In addition to his own declining health, news that his friend and mentor John Ford was dying of cancer forced the actor to consider his own mortality. After Ford's death in August of 1972, Wayne told reporters, "I'm pretty much living on borrowed time."
The anti-racism subtext was written into the script in response to ongoing criticism of John Wayne's infamous May 1971 interview with Playboy magazine. However, the only African-American in the cast, Vance Davis, is listed in the credits as "Negro".
After he finished the film, John Wayne went to Seattle, Washington, to film McQ (1974). Since Wayne was on location, Warner Bros. decided to hold the premiere of Cahill in Seattle in 1973. Protesters appeared at the opening claiming the film was unfair to Native Americans.