Ursula Kieran Reilly was born in Yonkers, New York, and raised in Westport, Connecticut, the daughter of Paul Reilly and Helen Kieran Reilly. Her mother was a mystery writer, as was her sister, Mary McMullen. Ursula Reilly's grandfather was James Michael Kieran, one-time president of Hunter College. Her uncle was journalist John Kieran. Ursula Reilly graduated from a Catholic girls' high school, Lauralton Hall in Milford, Connecticut.
