Before the Second World War, the territory in which Ajax is situated was a rural part of the township of Pickering. The town itself was first established in 1941 when a Defence Industries Limited (D.I.L.) shell plant was constructed and a townsite grew around the plant. By 1945 the plant had filled 40 million shells and employed over 9,000 people at peak production. It had its own water and sewage treatment plants, a school population of over 600, and of railroad and of roads. The entire D.I.L. plant site included some . People came from all over Canada to work at D.I.L.