Clark said she decided to run the distance of a marathon during every day of lockdown, expecting the project to last for about 15 days, but she kept it going, even finding time to run while moving to Naples, Fla.
Clark, who used a treadmill some days and ran outside when possible, ended up running 95 marathon distances in 95 days.
The runner said she had started a 96th marathon run, but decided to stop partway through when she felt ill.
"I always said that if I felt that I was going to be putting myself in a position of being a burden on the medical system, I would stop immediately," Clark told the Williams Record. "So as soon as things started going downhill, I pulled away from it."
Clark only later learned that she was experiencing symptoms of COVID-19.
"I was and am definitely proud to have the record, but I hope someone will go out and break it one day soon," she said.