Kirk Douglas turned down the role of Shaleen. Jack Palance desperately wanted the role but was never offered it.
Ann-Margret was first choice for the title role but turned it down.
Jane Fonda reportedly didn't understand the film when she read the script, but because she was under contract to Columbia Pictures at the time, she had no choice but to take the role of Cat Ballou.
Nat 'King' Cole died several months before the film was released.
Roy Chanslor's original novel was a serious western. The comedy elements were added for the film.
At his acceptance of the Oscar, Lee Marvin opened by saying, "Half of this probably belongs to a horse out in the Valley somewhere".
Like several other Columbia releases of the 1960s (i.e., Bye Bye Birdie, Strait-Jacket), this film includes a spoof of the studio logo, in this case with the Torch Lady doffing her robes in animation and turning into a cartoon cowgirl.
Ranked #10 on the American Film Institute's list of the 10 greatest films in the genre "Western" in June 2008.
The film's horse trainer told Elliot Silverstein that the scene where a horse leans against a wall with its front legs crossed could not be shot because horses don't cross their legs, then that it might be possible if he had a couple of days. Silverstein invoked his rank as director and gave him an hour. The trainer plied the horse with sugar cubes while repeatedly pushing its leg into position, and they were able to get the shot.
The painting in Sir Harry Percival's train carriage is not a Tintoretto. It is a Titian. The painting is a copy of Titian's "Sacred and Profane Love", painted c 1515. The original was purchased by Scipione Borghese in 1608 and is housed in the Galleria Borghese, Rome
This film inspired NBC to make two different pilots which aired on consecutive days in 1971. One pilot starred Lesley Ann Warren, and the other, Forrest Tucker.
When filming the scene where Kid Shaleen takes a bath and dons his costume, director Elliot Silverstein had all actions timed to the beat of a metronome, its pace increasing when Shaleen takes his guns. He planned to have the scene scored with Spanish guitars following this beat, but the producer was adamantly opposed to anything Spanish in a Western. In the end electric, guitars were used.