She was born in Cincinnati and moved with her family to Highlands, North Carolina, as a baby. She made her professional debut in Chicago as part of the improvisational group, The Compass Players, which included Mike Nichols, Elaine May, and Shelley Berman. Playing opposite Richard Basehart, Kevin McCarthy and William Hansen, Wilcox won the Clarence Derwent Award for her performance in The Day The Money Stopped by Maxwell Anderson and Brendan Gill, which lasted only three nights on Broadway in 1958. She starred in the 1961 play Look, We’ve Come Through with Burt Reynolds on Broadway. She replaced another actress in the 1963 revival of Eugene O’Neill’s Strange Interlude and then went on to do the 1965 play The Family Way, both on Broadway.

A life member of The Actors Studio, Wilcox is perhaps best known for her role in the 1962 film To Kill a Mockingbird, in which she played Mayella Violet Ewell, who falsely accuses Tom Robinson (Brock Peters) of raping her. Following that cinematic acting success, she performed two very memorable roles for television in 1964: The Twilight Zone episode “Number 12 Looks Just Like You” and the The Alfred Hitchcock Hour episode “The Jar” based on the Ray Bradbury short story. In 1974, she co-starred with Peter Falk and Robert Conrad in the Columbo episode An Exercise in Fatality. Wilcox remained active performing both on television and in films. Her final role was that of Mrs. Kline in the movie A Touch of Fate, which was released in 2003, six years before her death. She recalled receiving “unfriendly looks” when she showed up at a NAACP conference in Monterey, California, where an official had to remind participants that, “Collin is here at this conference because she believes in the cause. She is not the character in the film.”   On October 14, 2009, Wilcox died from brain cancer, aged 74, at her home in Highlands, North Carolina.  She is survived by her third husband, Scott Paxton, whom she married in 1979; three children, Kimberly Horne, Michael G. Paxton, and William Horne; and three grandchildren. She is also survived by her sister, Jeremy Wilcox, who still resides in Highlands, North Carolina.