Police in Livingston, Montana, said in a statement that officers were called to Kidder's home, where they found her dead.
"I read books", she told The Montana Standard in 2016, "and hung out with friends in the woods or at the hockey rink". Born in the Northwest Territories of Canada, she debuted in a short film about a logging town - and lit up the screen so much that by the age of 27, before Superman, she had acted in movies opposite Robert Redford, Peter Fonda and Gene Wilder. Her third marriage was to French director Philippe de Broca from 1983 to 1984. For fans of Yuletide terror, she memorably played the "bad girl" Barb in Black Christmas (1974).
The film, directed by Richard Donner, was one of the most expensive ever made to that point.
She wasn't the only "Smallville" star to speak out on social media about Kidder's death.
As news broke of Margot's death tonight, her Lois Lane Superman co-star Teri Hatcher took to Twitter to pen a heartfelt message.
After her breakout, Kidder appeared in scores of films while remaining in solid demand through the 1980s.
Kidder had numerous movies' most memorable lines, including "You've got me?!"
"She was kind of an indomitable person", she said in a phone interview. Actors Bud Collyer and George Reeves portrayed the Man of Steel, who disguises himself as Lane's nerdy, fumbling newsroom colleague Clark Kent. It was a very cheesy scene, but also oddly ideal.
Lois Lane became her iconic role, which she would reprise in all three sequels, though her relegation to a walk-on part in III was an imbecilic decision on the part of the writers (and Superman IV was simply an imbecilic decision). And, after watching Kidder, you will believe Lois backs down from no one. "Some of us made more of a fuss than others-me in particular-so you could tell the joy [of working together] in all our faces, in the first one in particular and half of the second one".
Christopher Reeve and Margot Kidder. She was confident and driven in a way women so rarely are allowed to be-because she never questioned herself, the film didn't question her either, and so she was never knocked down a peg or put into her "place", whatever the nebulous concept of a woman's "place" might be in any given scenario.
Kidder had a debilitating vehicle accident in 1990 that left her in a wheelchair for most of two years and made it hard to work. Kidder was born in Yellowknife because of her father's job, which required the family to live in remote locations.