Cook was born in Oshawa, Ontario and spent most of her life growing up in Whitby where she attended Anderson Collegiate Vocational Institute. Her father, Mike, is a teacher, and her mother, Sandra, works as a psychiatrist.She has three siblings, Nathan, Paul, and Angela. Cook is a member of The Church of Jesus Christ of Latter-day Saints. A dancer from age four, Cook began taking jazz, tap and ballet lessons. She danced competitively for many years, before deciding at the age of 16 that she wanted to try acting.