Monaghan was born in Winthrop, Iowa, the daughter of Sharon Monaghan (who ran a day care center in the family's home), and Bob Monaghan (a factory worker and part time farmer). She has two older brothers, Bob and John and her family frequently fostered and adopted children. She graduated from East Buchanan High School Class of 1994, where she was the class president and acted in a few plays. After graduation, she moved to Chicago to study journalism at Columbia College Chicago. Between studying, she did some modeling in the United States and in Milan, Singapore, Tokyo and Hong Kong. She left college with one semester remaining to move to New York to pursue modeling and acting.