Nancy Justine McKeon was born on April 4, 1966, in Westbury, New York to Donald McKeon, a travel agent, and Barbara McKeon. She began her entertainment career by modeling baby clothing for the Sears & Roebuck catalog when she was two. Along with her brother, Philip McKeon, she performed in many commercials. In 1976, her brother was chosen to play a major role on the television show, "Alice". It was then that the family moved from New York to Los Angeles.