At the time of the arrival of the Europeans in the 1600s, both
Algonquian-speaking peoples already lived in the
Credit River Valley area. One of the
First Nations groups the French traders found around the Credit River area were the Algonquian
Mississaugas, a tribe originally from the
Georgian Bay area. The name "Mississauga" comes from the
Anishinaabe word Misi-zaagiing, meaning "[Those at the] Great River-mouth." By 1700 the Mississaugas had driven away the
Iroquois, yet during the
Beaver Wars they played a neutral or post-emptive role.
Toronto Township, consisting of most of present-day Mississauga, was formed on 2 August 1805 when officials from York (what is now the City of Toronto) purchased 84,000 acres (340 km²) of land from the
Mississaugas. In January 2010, the Mississaugas and the federal government settled a land claim, in which the band of aboriginal people received $145,000,000, as
just compensation for their land and lost income.
The original villages (and some later incorporated towns) settled included:
Cooksville, Dixie, Erindale (called Springfield until 1890),
Port Credit, Sheridan and Summerville. This region would become known as Toronto Township. Part of northeast Mississauga, including the Airport lands and
Malton were part of Toronto Gore Township.
After the land was surveyed, the Crown gave much of it in the form of land grants to
United Empire Loyalists who emigrated from the
Thirteen Colonies during and after the
American Revolution, as well as loyalists from New Brunswick. A group of settlers from New York City arrived in the 1830s. The government wanted to compensate the Loyalists for property lost in the colonies and encourage development of what was considered frontier. In 1820, the government purchased additional land from the Mississaugas. Additional settlements were established, including: Barbertown, Britannia, Burnhamthorpe, Derry West,
Meadowvale Village, Mount Charles, and
Streetsville. European-Canadian growth led to the eventual displacement of the Mississaugas. In 1847, the government relocated them to
a reserve in the
Grand River Valley, near present-day
 In 1873, in light of the continued growth seen in this area much as a result of the many railway lines passing through the township which spurred on industry. The Toronto Township Council was formed to oversee the affairs of the various villages that were unincorporated at that time. The Council's responsibilities included road maintenance, and the constitution of a police force. Except for small villages, some
brickworks served by railway lines, most of present-day Mississauga was agricultural land, including fruit orchards, through much of the 19th and first half of the 20th century.
In the 1920s, cottages were constructed along the shores of
Lake Ontario as weekend getaway houses for city dwellers.
17 years later in 1937, 1,410.8 acres of land was sold to build the
Malton Airport (later known as the Pearson Airport). It became Canada's busiest airport which also put the end to the community of Elmbank.
Queen Elizabeth Way (QEW) highway, one of the first controlled access highways in the world, opened from Highway 27 to Highway 10 in Port Credit, in 1935 and later expanded to Hamilton and Niagara in 1939. The first prototypical suburban developments occurred around the same time, in the area south of the Dixie Road/QEW interchange. Development in general moved north and west from there over time and around established communities. Large-scale developments, such as Erin Mills and Meadowvale sprang up in the 1968 and 1969 respectively.
The township settlements of Lakeview, Cooksville, Lorne Park, Clarkson, Erindale, Sheridan, Dixie, Meadowvale Village, and
Malton were amalgamated by a somewhat unpopular provincial decree in 1968 to form the Town of Mississauga. At the time, both
Port Credit and
Streetsville were left out and remained as separate entities. A 1965 call for public input on naming the town received thousands of letters offering hundreds of different suggestions.
 The town name was chosen by plebiscite over "Sheridan". Political will, as well as a belief that a larger city would be a hegemony in Peel County, 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 10 November 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. 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 Mississauga, 218,000 people were evacuated.
Mississauga Civic Centre
seen from the south-east. This design was supposed to reflect the influence of farmsteads which once occupied much of Mississauga,
the architecture is based on a "futuristic farm" (the clock tower is the windmill, the main building on the top-right corner is the farmhouse, the cylindrical council chamber is the silo, and the building on the bottom left represents a barn)
Residents were allowed to return home, once the site was deemed safe. 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 modelled 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 recognise the charge details on their billings, as
Bell Canada continues to use the historic community exchanges: Clarkson, Cooksville, Malton, Port Credit, and Streetsville, rather than "Mississauga"; they are combined as a single Mississauga listing in the phone book.
Touch-Tone telephones were first introduced at Malton, the first in Canada, on 15 June 1964.
On 1 January 2010, Mississauga bought land from the Town of
Milton and expanded its border by 400 acres (1.6 km2) to Hwy. 407 affecting 25 residents.