Cavallari was born in Denver, Colorado, the second of three children of Judith Spies (née Eifrig) and Dennis Cavallari.[2][3] When her mother divorced her father, her older brother Mike moved with their father to Laguna Beach, California, while she moved with her mother to the village of Barrington, Illinois, a suburb an hour northwest of Chicago. After difficulties adjusting to a new life with a stepfather and stepbrother, Kristin moved to California to live with her father. Instead Kristin was enrolled at Santa Margarita Catholic High School for her freshman year. After she attended a Driver's Education course through Laguna Beach High School, her father enrolled her in LBHS.
