Douglas, a local beauty queen in her native Louisiana before becoming an actress, died on Thursday (local time) of pancreatic cancer at a hospital in Baton Rouge, her niece Charlene Smith said.
"The Beverly Hillbillies" ran on CBS for nine seasons - from 1962 to 1971 - and was one of the most popular shows of the 1960s, topping the ratings its first two seasons.
Douglas played the daughter of backcountry widower Jed Clampett, portrayed by Buddy Ebsen, who becomes rich when he discovers oil on his land, then moves his hillbilly family into a Beverly Hills mansion to live alongside the wealthy.
Elly May was gorgeous but was happier playing with her numerous pets including chimpanzees or "rasslin' fellas" rather than smooching them. Rich suitors tried to woo her with little success.
"Elly may not have kissed many fellows during the show's run, but she sure did kiss a heap of animals," Douglas told the Parsons Sun newspaper in Kansas in March.
Her co-stars included: Max Baer Jr. as big goofball cousin Jethro; Irene Ryan as irascible Granny; and Raymond Bailey as money-crazy banker Mr. Drysdale.
"Elly was a slice out of my life," Douglas added. "I was raised a tomboy, with one older brother and all male cousins. So I grew up swinging from vines and playing softball. I was getting ready for Jethro long before we ever met."
Douglas guest-starred on other shows including "Love, American Style" and "The Twilight Zone," but rejected some movie roles for being too racy.
Her only starring film appearance was in "Frankie and Johnny," a musical in which she played riverboat gambler Presley's girlfriend.
"She was a very giving person and a very Christian lady," her niece said.
Her agent, Jacqueline Stander, added, "She spent most of her time speaking to churches and other personal appearances and just spreading joy and love. She was a country angel."
Douglas in 2011 received a settlement to resolve her lawsuit against toymaker Mattel and CBS Consumer Products over a Barbie doll modeled after Elly May made without her permission. She unsuccessfully sued Disney in 1993, accusing the company of stealing her concept for the film "Sister Act."
