The Greater Toronto Area, commonly referred to as the GTA, includes the City of Toronto and the regional municipalities of Durham, Halton, Peel, and York. In total, the region contains 25 urban, suburban, and rural municipalities. The Greater Toronto Area begins in Burlington in Halton Region to the west, and extends along Lake Ontario past downtown Toronto eastward to Clarington in Durham Region. According to the 2021 census, the Census Metropolitan Area (CMA) of Toronto has a total population of 6.202 million residents, making it the nation's largest, and the 10th-largest in North America. However, the Greater Toronto Area, which is an economic area defined by the Government of Ontario[citation needed], includes communities that are not included in the CMA, as defined by Statistics Canada. Extrapolating the data for all 25 communities in the Greater Toronto Area from the 2021 Census, the total population for the economic region included 6,711,985 people.[citation needed] The Greater Toronto Area is a part of several larger areas in Southern Ontario. The area is also combined with the city of Hamilton to form a conurbation known as the Greater Toronto and Hamilton Area (GTHA).  The GTHA combined with Niagara Region form the core of the Golden Horseshoe. Etymology The term "Greater Toronto" was first used in writing as early as the 1900s although at the time, the term referred only to the old city of Toronto and to its immediate townships and villages, which became Metropolitan Toronto in 1954 and became the current city of Toronto in 1998. The use of the term involving the four surrounding regional municipalities came into formal use in the mid-1980s, when it was used in a widely discussed report on municipal governance restructuring in the region and was later made official as a provincial planning area. However, it did not come into everyday usage until the mid-to-late 1990s. In 2006, the term began to be supplanted in the field of spatial planning as provincial policy increasingly began to refer to either the "Greater Toronto and Hamilton Area" or the still-broader "Greater Golden Horseshoe". The latter includes the Greater Toronto Area's satellite municipalities, such as Peterborough, Barrie, Guelph, Kitchener, Waterloo, Cambridge and Niagara Region. The GTA continues, however, to be in official use elsewhere in the Government of Ontario, such as the Ministry of Finance. Census metropolitan area A map of Toronto's Census Metropolitan Area, which contains a large portion of the GTA Toronto is the central city of the Greater Toronto Area. Mississauga is the largest city in Peel Region and the second-largest city in the Greater Toronto Area. Brampton, also in Peel Region, is the third-largest city in the Greater Toronto Area. Markham is the largest city in York Region and the fourth-largest city in the Greater Toronto Area. See also: List of municipalities in the Greater Toronto Area Some municipalities considered part of the GTA are not within the Toronto Census Metropolitan Area (CMA), which is smaller than the land area and population of the GTA planning area. For example, Oshawa is the centre of its own CMA, yet deemed part of the Greater Toronto Area, while other municipalities, such as New Tecumseth in southern Simcoe County and Mono Township in Dufferin County are included in the Toronto CMA but not in the GTA.  These different border configurations result in the GTA's population being higher than the Toronto CMA by nearly one-half million people, often leading to confusion amongst people when trying to sort out Toronto's urban population. Other nearby urban areas, such as Hamilton, Barrie, St. Catharines-Niagara or Kitchener-Waterloo, are not part of the GTA or the Toronto CMA, but form their own CMAs near the GTA. Ultimately, all the aforementioned places are part of the Greater Golden Horseshoe metropolitan region, an urban agglomeration, which is the fifth most populous in North America. It is part of the Great Lakes megalopolis, containing an estimated 59.1 million people in 2011.

The first large influx of European settlers to settle the region were the United Empire Loyalists arriving after the American Revolution, when various individuals petitioned the Crown for land in and around the Toronto area. In 1787, the British negotiated the purchase of more than a quarter million acres (1,000 km2 [390 sq mi]) of land in the area of Toronto with the Mississaugas of New Credit. York County, would later be created by Governor John Graves Simcoe in 1792, which would at its largest size, comprise all of what is now Halton Region, Toronto, Peel Region, York Region and parts of Durham Region. The GTA saw three American incursions during the War of 1812. The Town of York (present-day Toronto) was attacked by American forces at Battle of York, on April 27, 1813; and was subsequently occupied until May 8. The second incursion occurred several months later, in July 1813, with two landings in the GTA. On July 29, American forces landed at Burlington Beach (present-day Burlington) in an attempt to dislodge British forces at the adjacent Burlington Heights.  However, finding the British forces too well-entrenched for any assault to be successful, the American naval force withdrew and proceeded east towards York. The American landings at York on July 31 went unopposed, with most of the soldiers garrisoned at York directed to defend Burlington Heights.  The third incursion occurred a year later, when an American naval squadron arrived outside of York's harbour on August 6, 1814. The squadron dispatched USS Lady of the Lake to enter the harbour in order to gauge the town's defences, where it briefly exchanged cannon fire with Fort York before withdrawing to rejoin the American squadron outside the harbour. American forces did not attempt a landing during this incursion, although remained outside York's harbour for three days before departing. In 1816, Wentworth County (which would later become the city of Hamilton) and Halton County were created from York County. York County would later serve as the setting for the beginnings of the Upper Canada Rebellion with William Lyon Mackenzie's armed march from Holland Landing towards York Township on Yonge Street, eventually leading up to the battle at Montgomery's Tavern. In 1851, Ontario County (present-day Durham Region) and Peel County were separated from York. Although the original boundaries of York County encompassed nearly all of the GTA, by 1851, its boundaries had been reduced to the present-day City of Toronto and York Region as depicted on the 1871 map. Since 1901 This article needs to be updated. Please help update this article to reflect recent events or newly available information. (August 2018) The idea towards a streamlined local government to control local infrastructure was made as early as 1907 by, William Findlay Maclean, a member of parliament and founder of The Toronto World, who called for the expansion of the government of the former City of Toronto in order to create a Greater Toronto. The idea for a single government municipality would not be seriously explored until the late 1940s when planners decided the city needed to incorporate its immediate suburbs. However, due to strong opposition from suburban politicians, a compromise was struck, which resulted in the creation of Metropolitan Toronto. In 1953, the portion of York County south of Steeles Avenue, a concession road which formed a common boundary between several townships across the width of the county, was severed from it and incorporated as the Municipality of Metropolitan Toronto. With the concession of Metro Toronto, the offices of York County were moved from Toronto to Newmarket. Originally, the membership in Metropolitan Toronto included the City of Toronto and five townships: East York, Etobicoke, North York, Scarborough and York; as well as seven villages and towns, which became amalgamated into their surrounding townships in 1967. The early Metro Toronto government debated over the annexation of surrounding townships of Markham, Pickering and Vaughan. Frederick Goldwin Gardiner, the first Metro Toronto Chairman, planned on the conversion of these townships into boroughs of the Metro Toronto government. In 1971, the remaining areas of York County was replaced by the Ontario government with the Regional Municipality of York. In 1974, Ontario and Durham Counties were reorganized to become the Regional Municipality of Durham; Pickering west of Rouge River was transferred to Scarborough at that time. Peel County became Peel Region in 1974 as well. In 1980, North York would be incorporated into a city, with York following suit in 1983 and Etobicoke and Scarborough in 1984, although still part of the Metropolitan Toronto municipal government. Satellite image of Toronto and Mississauga during the mid-1980s In 1992, the Ontario government passed legislation requiring Metropolitan Toronto to include the rest of the Greater Toronto Area into its planning. However, there was fear different parts of the municipal system were working against one another. Therefore, Bob Rae, the Premier of Ontario, appointed Anne Golden to head a GTA task force to govern the region's quality of life, competitiveness and governance. During this time, the Metro Toronto government advocated to the task force the creation of a new GTA authority, which would be made up of 21 of the 30 existing municipalities in the GTA at the time. The proposal from Metro Toronto would have resulted in 15 new municipalities. The City of Mississauga argued consolidation should take place only in such a way the new municipalities would have a population between 400,000 and 800,000. The Town of Markham had similarly advocated municipal consolidation in York Region but opposed to complete consolidation into a single municipality. Municipal consolidation faced stiff opposition, however. from smaller communities such as Ajax, Milton, and the borough of East York. The task force's recommendation to eliminate the Metro Toronto government, and consolidate its remaining municipalities into an enlarged City of Toronto was completed in 1997 and became official in 1998, under the Common Sense Revolution of the then premier, Mike Harris. However, the task force's recommendation to create a GTA-tier municipality was not taken up by the Harris government for fear that a GTA-wide municipality would recreate the intermunicipal competitiveness that was believed to have impaired the former Metro Toronto government. Metrolinx, an agency of the Government of Ontario, was established to oversee public transit development across the Greater Toronto Area.