Jennifer McCarthy was born to a middle-class Catholic family of Polish and Irish descent.
Jennifer Ann McCarthy was born at Little Company of Mary Hospital in Evergreen Park, Illinois, on November 1, 1972 in a working-class Catholic family. Her mother, Linda, was a housewife while her father, Dan McCarthy, worked in a steel mill. She grew up along with her three sisters, Lynette, Joanne, and Amy. The popular actress Melissa McCarthy is her cousin.