However, that didn't stop a lot of runners from finishing their own marathons wherever they could.
A "virtual marathon" included runners from all 50 states and more than 100 countries.
Some ran the original course, starting in Grant Park.
Others made up their own route, including first-time marathoner Mary Lu Seidel. Seidel mapped out her own 26.2 mile course on the city's south and west sides. She said her goal was to highlight historic landmarks that people might now know about.
"It's these more traditionally disinvested neighborhoods that have a really great history and communities that live there," Seidel said.
A Catholic priest also ran the virtual marathon on the North Side.
Father Michael Bradley mapped out a route that started and ended at St. Gertrude Church in Edgewater.
Parishioners and friends were there to cheer him on as he finished the run in 5 hours and 8 minutes.
Father Bradley's run raised more than $18,000 for the Heart to Heart ministry.
Sunday's run was his 20th Chicago marathon and 49th marathon overall.
Race organizers are still offering runners a way to pick their distance and submit results for a medal.
Organizers say the silver lining is that more people have been taking up running during the pandemic and they're already looking ahead to next year.