St. Catharines (2011 population 131,400; metropolitan population 392,184) is the largest city in Canada's Niagara Region and the sixth largest urban area in Ontario, with 96.11 square kilometres of land. It lies in Southern Ontario, 51 kilometres (32 mi) south of Toronto across Lake Ontario, and is 19 kilometres (12 mi) inland from the international boundary with the United States along the Niagara River. It is the northern entrance of the Welland Canal. Residents of St. Catharines are known as St. Cathariners.

St. Catharines carries the official nickname "The Garden City" due to its 1,000 acres (4 km2) of parks, gardens and trails.

St. Catharines is situated in an area for commerce and trade since it is located between the Greater Toronto Area (GTA) and the Fort Erie - US Border. Manufacturing is the city's dominant industry, as noted by the heraldic motto, "Industry and Liberality". General Motors of Canada, Ltd., the Canadian subsidiary of General Motors, was the city's largest employer, a distinction now held by the District School Board of Niagara. TRW Automotive operates a plant in the city, though in recent years employment there has shifted from heavy industry and manufacturing to services.

St. Catharines lies on one of the main telecommunications backbones between Canada and the United States, and as a result a number of call centres operate in the city.

The city was first settled by Loyalists in the 1780s. The Crown granted them land in compensation for their services and for losses in the United States. Early histories credit Serjeant Jacob Dittrick and Private John Hainer, formerly of Butler's Rangers, as among the first to come to the area. They took their Crown Patents where Dick's Creek and 12 Mile Creek merge, now the city centre of St. Catharines. Although never documented, some local St. Catharines historians speculate that Dick's Creek was named after Richard Pierpoint, a Black Loyalist and former American slave. Secondary to water routes, native trails provided transportation networks, resulting in the present-day radial road pattern from the City centre. The surrounding land was surveyed and Townships created between 1787 and 1789.

After the Butler's Rangers disbanded in 1784 and settled the area, Duncan Murray as a former Quartermaster in the 84th Regiment of Foot (Royal Highland Emigrants) was appointed by the Crown to distribute free Government supplies (victuals) for 2 years to the resettled Loyalists. He did this from his mill, built on the 12 Mile Creek in Power Glen. After his death in 1786, his holdings were forfeited to merchant Robert Hamilton of Queenston.

Hamilton tried to operate for profit the already well-established Murray's Distribution Centre and Mill under the management of his cousin. Among other ventures, Hamilton became land wealthy, expropriating lands from subsistence Loyalist settlers who were incapable of settling their debts. Murray's distribution centre, later Hamilton's warehouse, and its location have long been a mystery. Hamilton's major profits were derived from transhipping supplies for the military and civic establishments from his Queenston enterprise, not from charitably supplying the subsistence Loyalist settlers. Hamilton lacked interest in social development and sold his business to Jesse Thompson before the turn of the 18th century.

The small settlement was known as GǣThe TwelveGǥ and as GǣMurray's DistrictGǥ to military and civic officials, but the local residents in 1796 and earlier referred to it as St. Catharines.[8] This is confirmed in St. Catharines' first history, written by J.P. Merritt: Gǣto be historically accurate the name St. Catharines preceded all of theseGǪ.Gǥ

The Merritt family arrived after this time, among the later Loyalists to relocate following the American Revolution. They were from the Carolinas, New York state and New Brunswick. In 1796, Thomas Merritt arrived to build on his relationship with his former Commander and Queen's Ranger, John Graves Simcoe, now the Lieutenant Governor of Upper Canada.

At an unknown early date, an inn was built by Thomas Adams on the east side of what is now Ontario Street. It became a community meeting place, election centre, stagecoach stop, and mail delivery deposit. This was preceded by the church and a log school house completed before 1797, all located on the east bank of the 12 Mile Creek at the extreme west end of the what was known at that time as Main Street. This was an extension of the old Iroquois Trail and was renamed St. Paul Street by the settlers and descendant by the mid-19th century. Several mills, salt works, numerous retail outlets, a ship building yard, distillery and various other businesses were developed next.

The first Welland Canal was constructed from 1824 to 1833 behind what is now known as St. Paul Street, using Twelve Mile and Dick's Creek. William Hamilton Merritt worked to promote the ambitious venture, both by raising funds and by enlisting government support. The canal established St. Catharines as the hub of commerce and industry for the Niagara Peninsula.

Merritt also played a role in making St. Catharines a center of abolitionist activity. In 1855, the British Methodist Episcopal Church, Salem Chapel was established at the corner of Geneva and North streets, on land granted to the congregation by Merritt in the early 1840s. The area became known to refugee slaves from the United States as a place of "refuge and rest"; it was a destination, one of the final stops in Canada on the Underground Railroad for refugee African-American slaves. By the mid-1850s the town's population was about 6000, 800 of whom were "of African descent". St. Catharines remains an important place in Black Canadian history.

The Town of St. Catharines was incorporated in 1845. St. Catharines was incorporated as a city in 1876.

St. Catharines' development history has resulted in a number of unique and distinct communities within the city. The historical area of St. Catharines consisted of nothing more than what is now the downtown core, with the remaining land being part of Louth Township on the west and Grantham Township on the east. St. Catharines continued to steadily grow through the late 19th and early 20th centuries, eventually annexing land to the southwest that would become Western Hill and Old Glenridge, and to the east and north that would collectively become the central part of St. Catharines. In addition to the growth of St. Catharines, the Town of Merritton and the Town of Port Dalhousie existed as separate municipalities to the South and North of the city, each slowly growing their own residential base.

Along with the rest of Ontario, St. Catharines experienced explosive growth after World War II. St. Catharines continued to annex Grantham Township as development continued, including the large swaths of land to the north known now as "The North End". St. Catharines would also absorb Merritton and Port Dalhousie in 1961, making them part of the city. During this time, St. Catharines nearly tripled in population.

With the formation of the Regional Municipality of Niagara in 1970, the portion of Louth Township east of Fifteen Mile Creek was transferred to the City of St. Catharines. This included the eastern portion of the Hamlet of Rockway, as well as the Hamlet of Power Glen. The few remaining portions of Grantham Township in the Northeast corner of the area, including Port Weller, were also transferred to the city. With the new Louth Township lands belonging to the city, St. Catharines would begin two developments in the west end ' Martindale in 1983, and Vansickle in 1987. These developments are nearing completion. There was also a push to continue further expansion to the west in the late 1990s, but this has since been halted by Ontario Greenbelt legislation.