Highway 5 was quickly engulfed by the growing outer suburbs of Toronto in the 1950s and 1960s, which led to various portions being transferred to local jurisdiction (though still signed as connecting links) over the years.

South of the escarpment, at the western tip of Lake Ontario, is the Dundas district of Hamilton, which was once a separate town within the former Hamilton-Wentworth Region.

It passes through the rural hamlet of Rock Chapel, and then curves to the left on its final approach to Highway 6.

Under the orders of the first lieutenant governor of Upper Canada, John Graves Simcoe, Captain Samuel Smith led 100 of the Queen's Rangers to open a road from the head of Lake Ontario (now known as Dundas) to La Tranche (later London) in early 1791.

The first 32 kilometres (20 mi) from the lakehead to the Grand River—where the Mohawk village that was home to Joseph Brant was located—were blazed by the rangers by October 25, 1793.

These early trails "involved nothing more than clearing a corridor through the bush, leaving the bigger stumps to rot, often detouring around the really big trees.

[5] When the Department of Public Highways of Ontario (DPHO) began taking over the responsibility of roads in 1917, it did not assign route numbers.

Another set of roads were assumed through Wentworth on July 8, connecting with the portion in Haldimand County, through Hamilton to Clappison's Corners and east through Waterdown along Dundas Street.

A portion within York County was assumed through Etobicoke from its western boundary as far east as the village of Islington on July 29.

A final segment of Dundas Street, within Halton from Waterdown to what is now Winston Churchill Boulevard, was assumed on July 31.

[14] Within Wentworth County, the construction of the Clappison Cut through the Niagara Escarpment was underway by 1921, with the aim of bypassing the winding old route that is known today as Old Guelph Road.

[19] When the Hamilton–Jarvis Highway and Dundas Street were assumed by the province, they were paved from Islington village west to Summerville (near Dixie Road), but were otherwise gravel throughout.

[6][9][10] In 1923, the remainder of the route between Sixteen Mile Creek and Hamilton, including the new Clappison Cut, was paved.

[22] When the province assumed the remainder of the route to Paris, it began paving the highway west from Peters Corners.

The interchange opened along with the segment of Highway 403 south to the Queen Elizabeth Way at Ford Drive in mid-1981; the freeway was extended north to Erin Mills Parkway on November 17th of that year.

[32][33] Following the creation of Metropolitan Toronto on April 15, 1953,[34] the new municipality was given responsibility for most of the provincial highways that passed within its boundaries that were not already connecting links following streets urbanized prior to this time.

The sections of Highway 5 through Etobicoke and Scarborough were accordingly redesignated as connecting links and their maintenance given over to the new Metro government on January 15, 1954.

[citation needed] on November 27, 1991, a 1.2 kilometres (0.75 mi) segment of Dundas Street, from the interchange with Highway 403 east to Winston Churchill Boulevard, was made a connecting link through the municipal boundary area between Mississauga and Oakville, and maintenance was transferred to these municipalities.

[citation needed] As the connecting links were technically still part of Highway 5, shields continued to be posted along it and marked on the Official Ontario Road Map through Mississauga and Metropolitan Toronto up until 1998 when the highway designation was dropped altogether [37] As part of a series of budget cuts initiated by premier Mike Harris under his Common Sense Revolution platform in 1995, numerous highways deemed to no longer be of significance to the provincial network were downloaded to a lower level of government.

Studies, including an environmental assessment were conducted between 2004 and 2009, and settled upon a roundabout as the ideal replacement, with traffic signals at the two intersections with Westover Road (former Highway 52).