unty, kept Port Credit and Streetsville as independent island towns encircled by the Town of Mississauga. In 1974, both were annexed by Mississauga when it reincorporated as a city. That year, the sprawling Square One Shopping Centre opened, which has since expanded many times.
On November 10, 1979, a 106-car freight train derailed on the CP rail line while carrying explosive and poisonous chemicals just north of the intersection of Mavis Road and Dundas Street in Mississauga. One of the tank cars carrying propane exploded, and since other tank cars were carrying chlorine, the decision was made to evacuate nearby residents. With the possibility of a deadly cloud of chlorine gas spreading through suburban Mississauga, 218,000 people were evacuated. Within a few days Mississauga was practically a ghost town.
Later when the mess had been cleared and the danger neutralized residents were allowed to return to their homes. At the time, it was the largest peacetime evacuation in North American history. Due to the speed and efficiency in which it was conducted, many cities later studied and modeled their own emergency plans after Mississauga's. For many years afterwards, the name "Mississauga" was to Canadians associated with a major rail disaster.
North American telephone customers placing calls to Mississauga (and other post 1970 Ontario cities) may not recognize the charge details on their billings, as Bell Canada continues to use the former community names, rather than "Mississauga", to identify exchanges in the city: Clarkson, Cooksville, Malton, Port Credit, Streetsville.
On January 1, 2010, Mississauga bought land from the Town of Milton and expanded its border by 400 acres (1.6 km) to Hwy. 407 affecting 25 residents
