The fire destroyed 508 acres, burned the foliage off three mountains and drove off 49 of the refuge's 53 endangered California condors. Cash was unrepentant and claimed, "I don't care about your damn yellow buzzards." The federal government sued him and was awarded $125,172.

Cash met singer June Carter, of the famed Carter Family while on tour, and the two became infatuated with each other. In 1968, 13 years after they first met backstage at the Grand Ole Opry, Cash proposed to June, during a live performance in London, Ontario.

In 1967, "Jackson", a duet with his future wife June Carter, reached number two on the Billboard Country Singles chart and won a Grammy for Best Country & Western Performance Duet, Trio or Group.

On May 11, 1965, he was arrested in Starkville for trespassing late at night onto private property to pick flowers. He would later use this experience to write the song "Starkville City Jail".

Cash believed that his ancestry included Cherokee, which partly inspired his work on Bitter Tears. While initially reaching charts, this album met resistance from some fans and radio stations who rejected its "controversial" take on social issues.

In the introduction to Man in White, Cash writes about a reporter, who, interested in his religious beliefs, questioned whether the book was written from a Baptist, Catholic, or Jewish perspective. Cash replied "I'm a Christian. Don't put me in another box."

The song, written by humorist and poet Shel Silverstein, tells the tale of a young man's quest for revenge on a father who abandoned him at three years of age and whose only contribution to his entire life was naming him Sue.

In 1997, Cash was diagnosed with the neurodegenerative disease Shy-Drager syndrome. According to biographer Robert Hilburn, the disease was originally misdiagnosed as Parkinson's disease, and Cash even announced to his audience that he had Parkinson's after nearly collapsing on stage in Flint, Michigan. Soon afterwards, his diagnosis was changed to Shy-Drager, and Cash was told he had about 18 months to live. The diagnosis was later altered again to autonomic neuropathy associated with diabetes.

In 2007, JC Unit One was put on exhibit at the Rock and Roll Hall of Fame and Museum in Cleveland, Ohio.

His genre-spanning songs and sound embraced country, rock and roll, rockabilly, blues, folk, and gospel. This crossover appeal won Cash the rare honor of being inducted into the Country Music, Rock and Roll, and Gospel Music Halls of Fame.