O'Keefe was born in Cliffwood Beach, New Jersey, the daughter of Noreen, a housewife, and Jack O'Keefe, director of the Merck.She relations of Irish, Czech, Austrian, Polish and Swedish ancestry. As a child, the youngest of three sisters, she had a bowl cut and was herself described as a "loser." Her older sister was a model and she decided she wanted to do the same thing. She did, and said that the modeling work brought her more confidence and more friends. She attended a Catholic school and grew to be the shortest in the class to one of the highest in at least 5 feet 8 inches/1.73 meters, the height at which it is today.