Dermot Mulroney grew up in Alexandria, Virginia, and went to Maury Elementary School. He played the cello in school and city youth orchestras and acted in children's community theater. He made his high school stage debut in an awful play called "Are Teachers Human?" at George Washington Middle School. He graduated from T.C. Williams High School in 1981. His dad was a lawyer. He grew up with three brothers - Sean, Conor and Kieran Mulroney (now also an actor) - and a sister named Moira.