Keenan-Bolger was born in Detroit, Michigan. She is an alumna of the Mosaic Youth Theatre of Detroit and the Detroit School of Arts High School (formerly the Detroit High School for the Fine and Performing Arts). She is a graduate of the University of Michigan's musical theatre performance program. She is one of three children, all of whom are involved in the performing arts. Her brother, Andrew Keenan-Bolger, also graduated from the University of Michigan with a BFA in musical theatre in 2007. Already a Broadway veteran, Andrew joined the national touring company of The 25th Annual Putnam County Spelling Bee in the fall of 2007. Her sister, Maggie Keenan-Bolger, who wrote the noted play From the Inside, Out, studied theatre and gender and women's studies at Oberlin College and graduated in 2006.