 The Westfield High School Blue Devils compete in the Union County Interscholastic Athletic Conference, following a reorganization of sports leagues in Northern New Jersey by the New Jersey State Interscholastic Athletic Association (NJSIAA).With 1,398 students in grades 10–12, the school was classified by the NJSIAA for the 2015–16 school year as North II, Group IV for most athletic competition purposes, which included schools with an enrollment of 1,114 to 4,800 students in that grade range.Prior to the NJSIAA's 2010 realignment, the school had participated in the Watchung Conference, a high school sports association which consisted of public high schools covering Essex County, Hudson County and Union County.