Cook attended Heritage High School in Lynchburg, Virginia. He played running back, wide receiver and quarterback on offense, and cornerback on defense. He rushed for 789 yards and 12 touchdowns and caught 10 passes for 250 yards and three more scores as a senior, he also threw six TD passes. He was named first-team all-state defensive back as a junior when he made more than 50 tackles and intercepted eight passes. Considered a three-star by Rivals.com, Cook accepted a scholarship to Virginia over Virginia Tech.
Cook started 31-of-38 games for the Virginia Cavaliers, collecting 143 tackles with 5.5 tackles for loss, one forced fumble, one fumble recovery for a TD, 19 passes breakups and seven interceptions, two which he returned for TD's. His best season came as a senior, where he collected 40 tackles, including one stop for a three-yard loss, totaled a team-high four interceptions, one which he returned for a TD, and deflected six passes, including four on third down.