Jessica was the daughter of actor John Barrymore and his third wife Nina Wayne. John was estranged from daughter Drew Barrymore for many years before he passed away after suffering from cancer in 2004.
Drew, who was not a close relation, issued the following reaction to the news: "Although I only met her briefly, I wish her and her loved ones as much peace as possible. I'm so incredibly sorry for their loss."
Jessica was found surrounded by ''dozens of white pills" as she lay slumped behind the wheel of the vehicle, which was blocking the driveway of an apartment block in San Diego.
According to local station 10News, her body was discovered at 6am by residents who were trying to leave for work.
The Medical Examiner's Office later confirmed Jessica Barrymore’s identity to the station, and an autopsy has been scheduled to determine her cause of death.
Her last message, posted via her Facebook account, was a post from Mystera Magazine.
It read: "Life doesn't always introduce you to the people you want to meet.
"Sometimes, life puts you in touch with the people you need to meet to Help You, to Hurt You, to Guide You, to Leave You, to Love You, and to gradually Strengthen You into the Person You Were Meant to Become.[sic]"
Jessica had a history of drug and alcohol addiction and was admitted to a rehabilitation programme twice during her teens.
Her famous sister, Drew, also has a half-sister named Blyth.
Drew rose to fame at the age of six after she was cast in E.T. She has publicly discussed her own battle with drink and drugs, including admitting that she took cocaine for the first time aged 12.
At 13, she too had undergone rehabilitation treatment twice.