Up until World War II, Ajax was a rural farming area outside of Toronto and a part of the Pickering Township. In 1941, Defence Industries Limited (DIL) set up a munitions plant in this area. The creation of this plant lead to new jobs in the area and thus, the population of Ajax began to grow. After WWII, the population of Ajax continued to grow as more companies started moving there as well and the old DIL plant was transformed into classrooms and laboratories for the Ajax Division of the University of Toronto. In 1955, Ajax was incorporated into a town and in 1974, both it and parts of the Township of Pickering amalgamated as part of the creation of the Durham Region.