Paxton, an only child, was born in Woodland Hills, Los Angeles, California to what she has described as "a very mixed family." Her father, Steve Paxton, is a businessman of Irish and other European descent and is distantly related to actor Bill Paxton. Her mother, Lucia, is a dentist from Monterrey, Mexico, and as a result Paxton speaks some Spanish, although not fluently. Paxton's mother is Jewish and her father converted to Judaism upon marrying her mother. During her childhood, Paxton put on shows and wanted to perform, sometimes dressing up in costume and coming to school as a particular character. She grew up in the San Fernando Valley, chose to attend a public high school instead of accepting home-schooling, and graduated in June of 2006.