Ajax was established in 1941 to service a munitions plant built on a 1,200 ha site. It was named for one of the two British Leander-class cruisers that cornered the German pocket battleship Graf Spee in 1939. The streets within the town bear the names of the servicemen who served on the HMS Ajax and its sister ship the HMS Achilles.
After the Second World War, 7,300 returned servicemen took engineering courses offered in Ajax by the University of Toronto. After the Ajax campus closed, the site became home to thousands of refugees from post-war Europe. The "displaced persons (DP)" camp was in operation from 1949 to 1953. After its closure, Central Mortgage and Housing Corporation announced that Ajax would be Canada's first fully-planned industrial and residential centre.
Today the town is a light industrial centre. Ajax also functions as a bedroom community for Toronto. The earliest settlers in Pickering Village arrived in 1802. Several of its 19th-century buildings have been preserved including the Quaker Meeting House (c 1867) and a hotel (c 1850). This area now houses restaurants and quaint shops.