Trivia

John Wayne had met singer Karen Carpenter on a college show he hosted prior to the shooting of this movie. He was so impressed that he wanted Karen to audition for the role of Mattie Ross.
--Source: Little Girl Blue: The Life of Karen Carpenter, Page 49

John Wayne about his acting: “That was me letting myself having fun. For the first time i felt like an actor.”
--Source: John Wayne: The Man Behind the Myth, Page 293

The film takes place in Arkansas and Oklahoma, but was filmed in Colorado. Director Henry Hathaway: “Look, in Arkansas nobody's been ten miles from their house in their whole fucking lives. And when they see the picture, they'll be happy to know that some part of Arkansas looks like that.”
--Source: John Wayne: American, Page 563

Mia Farrow was approached to play Mattie, but she turned it down. Robert Mitchum had told her that Henry Hathaway was impossible to work with. Farrow wanted Roman Polanski to direct the film. She later said it was one of the biggest professional mistakes of her career.
--Source: John Wayne: American, Page 562

A film sequel, Rooster Cogburn, was produced from an original screenplay in 1975, with John Wayne reprising his role. A further made-for-television sequel entitled True Grit: A Further Adventure, appeared in 1978. In 2010 the Coen brothers directed a new adaptation of the novel, also called True grit.

When submitted for a rating from the MPAA in 1969, the film was given an "M". The film was edited and re-rated "G".

The only film for which John Wayne ever won an Oscar.

John Wayne had initially promised the role of Mattie Ross to his daughter Aissa Wayne, but director Henry Hathaway refused to cast her.

"Boeuf" means "Beef" in French.

Marguerite Roberts was a formerly blacklisted writer. John Wayne knew this before he read the script. He read it and liked it. He ignored people who said he shouldn't work on anything that a "blacklisted" writer wrote.

The gang's cave hideout (beds partially intact), snake pit, and various prop rocks can still be seen on private property outside Ouray, Colorado.

Kim Darby's character was supposed to be 14.

When he was making his True Grit, John Wayne was 61 years old. He was too unhealthy to perform his own stunts and, thanks to having an entire lung removed years prior, could barely walk more than 30 feet before heavy breathing.

John Wayne was disappointed by the casting of Kim Darby as Mattie Ross, and the two hardly spoke at all off camera. He later said, "Christ, talk about having no chemistry with your leading lady! She was the goddamn lousiest actress I ever worked with."