Mary Catherine McCormack (born February 8, 1969) is an American actress.

McCormack was born in Plainfield, New Jersey. She is the daughter of clinical therapist Norah and car dealership and ice cream parlor owner William McCormack. Her parents divorced in 1990. She has a sister Bridget, a professor of law at the University of Michigan Law School, and a brother William, an actor.

McCormack graduated from The Wardlaw-Hartridge School in Edison, New Jersey, in 1987 and went on to attend, but never graduate from, Trinity College in Hartford, Connecticut, majoring in English and painting.