"It is with considerable sadness that we share that our wife, mother and grandmother died at 8:25am (PT) this morning," said a statement on the Terry Fox Foundation website that was signed by "Rolly, Fred, Darrell and Judi."
"Betty/Mom passed away peacefully surrounded by love. Betty was comfortable the last few weeks and months of her life, was always full of wit and rarely alone. Betty is now with Terry and joins other dear family members that predeceased her."
The family made it public earlier this month that Fox, who was in her 70s, was seriously ill, after a media report surfaced, stating she had cancer.
Tributes flowed at the time. While her family confirmed that she was seriously ill, they said then that she was not suffering from cancer, the disease that claimed her famous son.
They declined to release any other details.
Terry Fox has become known around the world after running more than 5,000 kilometres across half the country on a leg amputated after a cancer diagnosis.
Diagnosed when he was 18, Fox set out two years later to raise money for cancer research, leaving St. John's in April 1980, and running 42 kilometres a day until he was forced to stop near Thunder Bay, Ont., when cancer appeared in his lungs. He died on June 28, 1981, at age 22.
After Terry's death, the Fox family worked to keep organizing annual marathons. The Terry Fox Foundation was officially registered in 1988 and has raised more than $550 million for cancer research.
Rick Hansen — a gold medal-winning Paralympian who undertook his own global marathon in support of athletes with disabilities — on Friday earlier this month called Betty Fox a "remarkable" person.
"She and the entire Fox family have been tremendous friends to me on my own life journey," he told Postmedia News in an email.