When Johnny Cash wakes up on the tour bus, just after the Folsom Prison performance, he walks past guitarist Luther Perkins, who is passed out with a lit cigarette in his mouth, and puts the cigarette out. Perkins died a few months after the "At Folsom Prison" recording and performance. He fell asleep in his Tennessee house with a lit cigarette in his mouth, and died from injuries sustained in the resulting fire.

Joaquin Phoenix and Reese Witherspoon performed all of the songs themselves, without being dubbed. They also learned to play their instruments (guitar and auto-harp, respectively) from scratch.

Co-writer and director James Mangold said that Joaquin Phoenix and Reese Witherspoon developed a very codependent relationship during filming. According to him, after the filming wrapped, Phoenix admitted to him that he and Witherspoon had relied on each other so much that they made a secret pact. The deal was that if one of them left or dropped out, the other would leave as well.

During one scene, Johnny Cash is high and performing "I Got Stripes", he walks right up to June Carter and glares at her for an uncomfortably long period of time on-stage. According to co-writer and director James Mangold, this was unscripted and improvised by Phoenix and Witherspoon. Mangold said that he simply told Joaquin Phoenix to do what he would do in real life if he were angry at his girlfriend and then had to perform on stage with her. Much to Phoenix's surprise, this backfired and Reese Witherspoon responded to his actions by simply rolling her eyes, and continuing to perform the song. Phoenix later said that her reaction threw him off because his goal had been to make her as uncomfortable as possible on-stage.

The film was screened for the inmates of Folsom Prison, thirty-eight years after Johnny Cash's landmark performance.