Larson was born in Minneapolis, Minnesota, the daughter of Ruth Evangeline (née Boyce), an interior decorator, and John Charles Larson, an aerospace engineer. She has three sisters. Larson attended the same high school as Dorothy Lyman, who played Opal on All My Children before her. She enrolled at the University of Minnesota (eventually, she finished her education at Hunter College), and began singing in nightclubs with a group called Just Us. It was not long before Just Us was discovered and headed to New York City, where they recorded several soundtracks, including the one for the film, Rachel, Rachel, starring Joanne Woodward.