The Millville Senior High School Thunderbolts compete in the Atlantic Division of the Cape-Atlantic League, an athletic conference comprised of parochial and public high schools located in Atlantic, Cape May, Cumberland and Gloucester counties that operates under the supervision of the New Jersey State Interscholastic Athletic Association (NJSIAA). With 1,260 students in grades 10-12, the school was classified by the NJSIAA for the 2019–20 school year as Group IV for most athletic competition purposes, which included schools with an enrollment of 1,060 to 5,049 students in that grade range. The football team competes in the Continental Division of the 95-team West Jersey Football League superconference and was classified by the NJSIAA as Group IV South for football for 2018–2020.