King's Highway 24, commonly referred to as Highway 24, is a highway in the Canadian province of Ontario that currently begins at Highway 3 in Simcoe, and ends at the southern city limits of Cambridge. The south–north route travels through Brantford, as well as the community of Scotland. Outside of those communities, Highway 24 travels through a predominantly agricultural area.

Highway 24 was established in 1927 between Simcoe and Guelph. Between 1936 and 1938, it was extended northeast to Collingwood, as well as south from Simcoe to Port Dover. Much of the section of highway between Caledon Village and Collingwood followed Hurontario Street (partially as a concurrency with Highway 10), with the section of that historic route from Orangeville and Glen Huron being bypassed. Construction of a new route between Simcoe and Brantford took place in the mid-1960s, bypassing the town of Waterford.

In 1997 and 1998, the majority of Highway 24 – both south of Simcoe, as well as north of and through Cambridge – was transferred to the responsibility of the various counties and regions through which it travelled. The former sections of the route are now known as Norfolk County Highway 24, Waterloo Regional Road 24, Peel Regional Road 24, and County Road 124 in Wellington, Dufferin, Grey and Simcoe Counties.

Highway 24 begins at Highway 3 in the town of Simcoe. The highway once continued south, but this has since been transferred to local jurisdiction and is now Norfolk County Highway 24. Within Simcoe, it is maintained under a Connecting Link agreement for approximately 2.5 kilometres (1.6 mi). North of the town, Highway 24 travels in a straight line northward through Norfolk County, with farmland dominating the surroundings. As the highway approaches the community of Scotland, it enters Brant County. It turns northeast and bypasses to the east of the community, then meanders through thick forests for several kilometres. It returns to farmland and curves northward before intersecting former Highway 53 (Colborne Street West) near Brantford Municipal Airport.

A short distance north of former Highway 53, which is now known as Brant County Highway 53, Highway 24 encounters an interchange with Highway 403 (Exit 27) south of Paris. The route joins concurrently with Highway 403 for 9 kilometres (5.6 mi) east into Brantford. Highway 24 splits from Highway 403 to resume its northward orientation at the King George Road interchange (Exit 36). The highway is maintained under a Connecting Link agreement for 2.2 kilometres (1.4 mi) north of Highway 403, serving as a principal business route through the northern portion of the city. Between Brantford and Cambridge, Highway 24 is a busy two lane rural highway that has played host to frequent collisions, prompting a Ministry of Transportation of Ontario (MTO) investigation into possible upgrades to the stretch.

Highway 24 is generally straight and flat as it progresses north through the agricultural countryside of Brant County, but suddenly drops into the Grand River Valley as it enters the Regional Municipality of Waterloo. It follows the river along its eastern bank towards Cambridge, ending at the southern city limits. Within Wellington, Dufferin, Grey and Simcoe counties, the former route of Highway 24 is now designated as County Highway 124, while in Waterloo and Peel Regions the route is designated Regional Road 24. Within Wellington County, there is also an unrelated County Road 24.

Highway 24 was first designated on July 2, 1927, when the Department of Highways (DHO) assumed the road between Highway 3 at Simcoe and Highway 2 in Brantford, as well as the road connecting Highway 2 in Paris with Highway 6 in Guelph, via Galt (Cambridge), as a new provincial highway. In addition, a concurrency was established with Highway 2 between Brantford and Paris. Highway 24 originally entered Brantford along Mount Pleasant Street, before turning northeast onto Oxford Street (renamed Colborne Street West circa 1947), thence northwest concurrently with Highway 2 (Brant Avenue / Paris Road) to Paris. At Church Street in Paris, it branched from Highway 2 north along Dumfries Street and then Grand River Street towards Cambridge. On June 4, 1930 a more direct routing between Brantford and Cambridge was established; the route between Paris and Cambridge was renumbered as Highway 24A. As a result, the concurrency between Highway 2 and Highway 24 was reduced, with Highway 24 now departing Highway 2 in Brantford, along St. Paul Avenue and King George Road.

On September 9, 1936, the highway was extended south from Simcoe to Lake Erie then east to Highway 6 in Port Dover. This was followed several months later by an extension from Guelph through Erin to the Wellington–Peel county boundary, which was assumed on March 31, 1937. On August 11, 1937, the DHO designated the Shelburne to Collingwood Road as Highway 24. The highway turned east at Singhampton and continued to near Glen Huron, where it curved back north to rejoin Hurontario Street until its terminus in Collingwood. This left a large gap in the highway, including the terminus near Erin that did not end at a provincial highway. This was remedied eight months later when the DHO assumed several county roads in Peel County (now the Regional Municipality of Peel) on April 13, 1938. This established Highway 24 between the county boundary and Orangeville, via Alton, as well as Highway 51 between Highway 10 in Caledon Village and Coulterville. In addition, Highway 10 and Highway 24 were signed concurrently between Orangeville and Shelburne. By 1963, the segment of Highway 24 through Alton was redesignated as Highway 136, as Highway 24 was re-routed along a redesignated Highway 51 towards Highway 10 in that year.

Construction of a new route for Highway 24 between Simcoe and Brantford began on October 9, 1963. While originally intended to be an extension of Highway 24A between Simcoe and Paris, it would instead serve as a rerouting of Highway 24 upon completion as far north as the Highway 53 junction south of Paris by 1968. In 1970, the southern terminus of Highway 24 was rerouted southwest to end at Highway 59 near Walsingham, with Highway 6 absorbing the short length west of Port Dover to Halfway House Corner.

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 decommissioned and responsibility for the routes transferred to a lower level of government, a process referred to as downloading. Portions of Highway 24 were consequently transferred to local jurisdictions in 1997 and 1998. On April 1, 1997, the southernmost section, between Highway 59 and Highway 3 at Simcoe, was transferred to Norfolk County. On January 1, 1998, the section north of Cambridge, through Waterloo and onward to Collingwood, was transferred to the various counties and regions through which it travelled.

The following table lists the major junctions along Highway 24, as noted by the Ministry of Transportation of Ontario. 

Division	Location	km	mi	Exit	Destinations	Notes
Norfolk	Walsingham	−32.1	−19.9		County Road 60 west  Norfolk County Highway 24 begins  County Highway 59 – Port Rowan, Tillsonburg	Former Highway 24 southern terminus; formerly Highway 59
	Halfway House Corner	−7.0	−4.3		County Highway 6 east – Port Dover	Formerly Highway 6 north
	Simcoe	−1.0	−0.62		County Road 1 west (Robinson Street) / Argyle Street
		0.0	0.0		Highway 24 begins  Norfolk County Highway 24 ends  Highway 3 – Delhi, Jarvis	Highway 24 southern terminus; beginning of Simcoe Connecting Link agreement
		0.4	0.25		County Road 35 west (Second Avenue)
		1.2	0.75		County Road 40 west (14th Street)
		2.5	1.6			End of Simcoe Connecting Link agreement
		3.7	2.3		County Road 24 north (Old Highway 24) – Waterford
		8.3	5.2		County Road 9 east (Thompson Road) – Waterford
		9.6	6.0		County Road 9 west (Windham Centre Road) – Windham Centre
		14.9	9.3		County Road 19 west
		15.2	9.4		County Road 19 east
Brant	Scotland	19.7	12.2		County Road 4 west (Vanessa Road)
		20.9	13.0		County Road 4 (Oakland Road)
		30.4	18.9		County Road 12 east (Arthur Road)
		31.2	19.4		County Highway 53 (Colborne Street West) – Burford, Brantford	Formerly Highway 53; near Brantford Airport
		36.0	22.4	27	County Highway 24 north (Rest Acres Road) – Paris  Highway 403 west – London	Southern end of Highway 403 concurrency; exit numbers follow Highway 403
Brantford		39.5	24.5	30	County Road 27 (Oak Park Road)
		42.4	26.3	33	County Highway 2 (Paris Road) – Paris	Formerly Highway 2
		45.0	28.0	36	Highway 403 east – Hamilton King George Road	Northern end of Highway 403 concurrency; beginning of Brantford Connecting Link
		47.2	29.3		Powerline Road	End of Brantford Connecting Link
Brant	Osborne Corners	49.2	30.6		County Highway 5 west / County Highway 99 east (Governors Road E) – Paris, Hamilton	Formerly Highway 5 west / Highway 99 east; former southern end of Highway 5 concurrency
		52.7	32.7		County Highway 5 east – Burlington  County Road 35 west (Blue Lake Road)	Formerly Highway 5 east; former northern end of Highway 5 concurrency
Brant–Waterloo boundary	North Dumfries	59.3	36.8		County Road 144 east (Lockie Road)
Waterloo		59.7	37.1		Regional Road 45 south (East River Road)	To Brant County Road 14
	Cambridge	64.1	39.8		Highway 24 ends  Waterloo Regional Road 24 begins  Regional Road 81 east (McQueen Shaver Boulevard)	Cambridge city limits; Highway 24 northern terminus
		68.7	42.7		Regional Road 8 (Coronation Boulevard)	Formerly Highway 8
		73.3	45.5		Highway 401 – London, Toronto	Highway 401 exit 282
Waterloo–Wellington boundary	Cambridge–Woolwich–Guelph/Eramosa boundary	80.4	50.0		Waterloo Regional Road 24 ends  Wellington County Road 124 begins  Regional Road 31 west (Kossuth Road)
Wellington	Guelph/Eramosa			No major junctions
Guelph		86.8	53.9		Wellington County Road 124 breaks Fife Road	Guelph city limits
		87.8	54.6		Highway 6 / Highway 7 west (Hanlon Expressway) to Highway 401 – Mount Forest, Hamilton	Interchange; former southern end of Highway 7 concurrency
		90.3	56.1		Highway 7 east (Wyndham Street South) – Acton	Former northern end of Highway 7 concurrency
Wellington	Guelph/Eramosa	95.3	59.2		Wellington County Road 124 resumes	Guelph city limits
	Erin	111.2	69.1		County Road 125 south	Ospringe; formerly Highway 25 south; former southern end of Highway 25 concurrency
		118.1	73.4		County Road 24	Brisbane; formerly Highway 25 north; former northern end of Highway 25 concurrency
Wellington–Peel boundary	Erin–Caledon boundary	126.2	78.4		Wellington County Road 124 ends  Peel Regional Road 24 begins  Wellington County Road 25 / Peel Regional Road 19 (Winston Churchill Boulevard)
Peel	Caledon	130.3	81.0		Regional Road 136 north (Main Street) – Alton	Coulterville; formerly Highway 136 north
		134.5	83.6		Highway 10 (Hurontario Street) – Orangeville, Brampton  Regional Road 24 east (Charleston Sideroad)	Caledon Village; formerly Highway 24 northern terminus; Regional Road 24 continues east
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Closed/former       Concurrency terminus       Route transition

Highway 24A
Location	Paris – Bannister Lake Complex
Length	7.6 km (4.7 mi)
Existed	June 4, 1930–April 1, 1997