The Northern Valley Regional High School at Demarest Norsemen compete in the Big North Conference, a super-conference comprised of public and private high schools in Bergen and Passaic counties established in 2009 as part of an effort to achieve greater competitive balance between schools, following a reorganization of sports leagues in Northern New Jersey by the New Jersey State Interscholastic Athletic Association. The school had previously competed in the North Bergen Interscholastic Athletic League, an athletic conference that consisted of high schools located in Bergen County. With 762 students in grades 10-12, the school was classified by the NJSIAA for the 2019–20 school year as Group III for most athletic competition purposes, which included schools with an enrollment of 761 to 1,058 students in that grade range. The football team competes in the Patriot Red division of the North Jersey Super Football Conference, which includes 112 schools competing in 20 divisions, making it the nation's biggest football-only high school sports league. The school was classified by the NJSIAA as Group III North for football for 2018–2020.