The highway once continued east to Yonge Street in Newmarket, but is now known as York Regional Road 31.

It was extended to Cookstown in the early 1930s via Orangeville and Shelburne, creating a short lived concurrency with Highway 10.

The highway continues in this direction through the villages of Clifford and Harriston, forming the centre of a thin band of farmland oriented at a 45-degree angle to the surrounding land.

The highway once continued east to Yonge Street in Newmarket, but this section is known as York Regional Road 31.

[4][5] The western section from Kincardine to Walkerton is today Highway 9, and the other sections to the east were at one point part of Highway 4, and today Bruce County Road 4 and Grey County Road 4.

By October 1963, Davis Drive was built west of Newmarket, across the Holland Marsh to Schomberg.

On July 23, 1965, Highway 9 was extended to Newmarket along Davis Drive, bringing its total length to 191.7 km (119.1 mi).

At the same time, Highway 9 was rerouted from its straight route to meet the new bypass, creating Buena Vista Drive as a result.

Starting in 1978, numerous plans were formulated for a southern bypass of Broadway, none of which came to fruition.

[16] The following table lists the major junctions along Highway 9, as noted by the Ministry of Transportation of Ontario.