Molly Glynn, 46, was cycling with her husband, Joe Foust, in a forest park in Chicago when they got caught in a violent thunderstorm.
READ: HOW TO DEAL WITH GRIEF AND SEPARATION
The sudden change in weather caught them by surprise and, as they were attempting to cycle to safety, a tree slammed into the actress.
She was taken to Evanston Hospital in Chicago, where she died from her injuries on Saturday.
Her heartbroken husband revealed the sad news to friends, family and fans via Facebook.
He wrote: "Friends, this is the darkest day of my life. Things will never be the same. Molly got hit by a falling tree while we were biking. At hospital now. Prognosis is grim.
"I couldn't save her. I couldn't save her. She's gone."
David Rice, the executive director of First Folio Theatre and a close family friend, said: "Molly was one of the most loving and generous people in the Chicago theatre scene.
"She was incredibly talented — incredibly versatile. She could handle both comedy and the deepest darkest, dramas.
"It was a freak accident and a matter of being in the wrong place at the wrong time."
READ: 50 INSPIRATIONAL LIFE LESSONS TO SHARE WITH THE IMPORTANT PEOPLE IN YOUR LIFE
Others in the theater community in and around Chicago also expressed shock and sadness.
"It is an incalculable loss," said Michael Halberstam, the artistic director of the Glencoe-based Writers Theatre.
"She was a loving mother and wife and everyone who met her fell in love with her."
READ: INSPIRATIONAL QUOTES ON DEALING WITH GRIEF
On Friday, a crowd funding campaign was launched on GiveForward.com by Glynn's friends to raise money for Glynn's widower and her two teenage sons from a previous marriage.
So far, the campaign had raised $120,793 (£74,689) of its $125,000 (£77,258) goal.
Our thoughts are with her family at this difficult time.