Monaghan was born in
Winthrop, Iowa, the daughter of Sharon (née Hammel),
 who ran a day care center in the family's home for forty years,
 and Robert Monaghan, a factory worker.
 She has two older brothers, Bob and John.
 Monaghan has Irish and German ancestry, and was raised
She graduated from
East Buchanan High School in 1994,
 where she was class president and acted in several plays.
 After graduation, she moved to Chicago to study journalism at
Columbia College Chicago and began to
 She modeled in
Hong Kong, as well as in the United States. With one semester remaining to complete her journalism degree in 1999, she left for New York to pursue an acting career, where she appeared as a model in several magazines and catalogs before making her acting debut.