This picture marked the return of John Wayne to work after having a cancerous lung removed just four months earlier. He insisted on doing all his own stunts to show the public that the illness hadn't slowed him down.
Despite this being a big budget movie with a large cast, Karl Swenson was utilized to play two parts. He played "Doc Isdell" and also the bartender in the scene where the Dean Martin character auctioned his eye. The bartender part actually had more lines of dialogue.
Filming was due to begin in September 1964, but had to be delayed until January 1965 after Wayne was diagnosed with lung cancer.
According to her tombstone, Katie Elder was 64 when she died. Her eldest son is played by 57-year-old John Wayne.
When John Wayne is dragged into the river, you can hear a child calling out, "Dad!". This was his three-year-old son Ethan Wayne, who was watching off camera and knew how ill his father was.
In western history, there is a famous Katie Elder: "Big Nose" Kate Elder, a prostitute and girlfriend of legendary gunfighter John "Doc" Holliday.
The hearse featured at the funeral of Katie Elder currently resides in front of the Haunted Mansion at Walt Disney World.