She will be replaced by her understudy, Linda Mugleston. Into the Woods closes Dec. 29 after 18 previews and 279 regular performances.
Williams is the second major cast member to leave the Stephen Sondheim-James Lapine tuner. Laura Benanti, who starred as Cinderella, left the show in early October. The Boys from Syracuse star Erin Dilly replaced her in the role. The show won the 2002 Tony Award for Best Revival (Musical).
Billed as a family show, Into the Woods twists popular fairy tales, infusing them with an adult sense of what happens after the "Happily Ever After." Jack's murder of the giant (of beanstalk fame) provokes the wrath of his giant wife, Cinderella's prince is a hopeless philanderer, the witch is not wicked but overprotective, and a slightly psychotic Little Red Riding Hood proudly wears the grey skin of the wolf she cut up from the inside out. The score is one of Sondheim's most popular, with the comic and manic "Into the Woods," "Agony" and "On the Steps of the Palace" contrasting with the dramatic and wondering "Children Will Listen" and "Giants in the Sky."