The Chatham High School Cougars compete in the Northwest Jersey Athletic Conference, which is comprised of public and private high schools in Morris, Sussex and Warren counties, and was established following a reorganization of sports leagues in Northern New Jersey by the New Jersey State Interscholastic Athletic Association (NJSIAA). Prior to the NJSIAA's 2010 realignment, the school had competed as part of the Iron Hills Conference, comprised of public and private high schools in Essex County and Union County.
The Chatham High School Cougars are affiliated with the Northwest Jersey Athletic Conference, a league that encompasses both public and private high schools across Morris, Sussex, and Warren counties. Prior to 2010 realignment, they were part of the Iron Hills Conference, which included schools from Essex County and Union County.