When the school opened, the Earl of March's catchment area was a large part of the Regional Municipality of Ottawa–Carleton, encompassing March, Huntley, Torbolton, and Fitzroy townships and part of Goulbourn Township. As such, Earl of March served for many years as the sole high school for Ottawa's then-nascent northwestern suburbs outside the Greenbelt. As Kanata started to rapidly expand in the late 1970s to the 1990s, other high schools were built and the catchment area was made smaller to prevent excessive over-crowding. Today, the Earl of March is one of five public high schools, three Catholic high schools, and several private high schools that now facilitate the area the Earl used to.