Born in Dallas, Texas and raised in Toms River, New Jersey, Perabo is the child of Mary Charlotte (née Ulland), a physical therapist, and George William Perabo, a lecturer in poetry at Ocean County College. She is of English, German, and Irish (father) and Norwegian (mother) descent; her surname is sometimes mistakenly described as Portuguese.
Perabo's parents named her after actress Piper Laurie. She is the eldest of three children with two brothers, Noah and Adam. She graduated from Toms River High School North in 1994, and earned a bachelor's degree in theater from Honors Tutorial College at Ohio University in 1998. In 1996, she attended the Trinity/La MaMa Performing Arts Program. She also studied Latin, physics, and poetry in her final year.
Perabo was first noticed a year before she graduated from college. She was in New York City, visiting her then-boyfriend, and accompanied him to an audition. Casting director Denise Fitzgerald spotted her and asked her to read for a part. She was not cast, but when Fitzgerald found out that she did not have any representation, she made phone calls on Perabo's behalf and found her an agent.
