Jett is the daughter of country music icon Hank Williams, Sr. and Bobbie Jett, whose brief relationship with Hank Williams occurred between his two marriages. She is a posthumous child; her birth in Montgomery, Alabama occurred five days after her father's death. She was legally adopted by Hank Williams' mother Lillian in December 1954. Lillian had already named her Catherine Yvonne Stone. After Lillian died in 1955 the young Cathy was made a ward of the state of Alabama and subsequently adopted by new parents who renamed her Cathy Louise Deupree.
Jett knew she was adopted but it was not until the early 1980s that she learned who her biological parents were. Although Hank Williams had executed a pre-birth custody agreement three months before her birth that gave him custody of his unborn daughter, she was forced to go to extreme lengths to prove the relationship and be recognized as Williams' daughter. She was reportedly very slow to be accepted as kin by her half-brother, country music icon Hank Williams, Jr.
In 1985 the Alabama State Court ruled that she was the daughter of Hank Williams, and in 1987 the Supreme Court of Alabama ruled that she was entitled to her half-share in the Williams estate, as she had been the victim of fraud and judicial error.
In 1990 she published her autobiography Ain't Nothin' as Sweet as my Baby.
In February 2005 the Tennessee Court of Appeals upheld a lower court ruling stating that Hank Williams' heirs — son Randall Hank Williams and daughter Jett Williams — have the sole rights to sell his old recordings made for a Nashville radio station in the early '50s. The court rejected claims made by Polygram Records and Legacy Entertainment in releasing recordings Williams made for the "Mother's Best Flour Show," a program that originally aired on WSM-AM. The recordings, which Legacy Entertainment acquired in 1997, include live versions of Williams' hits and his cover version of other songs. Polygram contended that Williams' contract with MGM Records, which Polygram now owns, gave them rights to release the radio recordings.