Fox was born on May 16, 1986 in Oak Ridge, Tennessee, the daughter of Gloria Darlene (née Cisson) and Franklin Thomas Fox, a parole officer. She is mostly of English ancestry, with smaller amounts of ancestry from elsewhere in Europe. She was raised "very strictly Pentecostal", but later attended Catholic school for twelve years. Fox's parents divorced when she was young. Fox's mother later remarried, and she and her sister were raised by her mother and her stepfather, Tony Tonachio. She said that the two were "very strict" and that she was not allowed to have a boyfriend[13] or invite friends to her house. She lived with her mother until she made enough money to support herself.
Fox began her training in dance and drama at age five, in Kingston, Tennessee. She attended a dance class at the community center there and was involved in Kingston Elementary School's chorus and the Kingston Clippers swim team. At 10 years of age, after moving toSt. Petersburg, Florida, Fox continued her training. When she was 13 years old, Fox began modeling after winning several awards at the 1999 American Modeling and Talent Convention in Hilton Head, South Carolina. At age 17, she tested out of school via correspondence in order to move to Los Angeles, California.
Fox has spoken extensively of her time in education; that in middle school she was bullied and picked on and she ate lunch in the bathroom to avoid being "pelted with ketchup packets". She said that the problem was not her looks, but that she had "always gotten along better with boys" and that "rubbed some people the wrong way". Fox also said of high school that she was never popular and that "everyone hated me, and I was a total outcast, my friends were always guys, I have a very aggressive personality, and girls didn’t like me for that. I’ve had only one great girlfriend my whole life".[18] In the same interview, she mentions that she hated school and has never been "a big believer in formal education" and that "the education I was getting seemed irrelevant. So, I was sort of checked out on that part of it".