In 1928, the route was extended south into Burlington, following portions of Lower Middle Road to Highway 2.

The route remained relatively unchanged for two decades, save for the southern end being truncated at the QEW in 1946.

The entire route was decommissioned in 1997 and 1998 as part of a province-wide downloading of highways deemed to be of regional importance.

It passed through the rolling hillside of Halton Hills into the community of Acton, where it encountered Highway 7.

North of that town, it continued through rolling farmland before ending at Highway 89 west of Shelburne.

[4] The history of Highway 25 dates back to 1925 when the Department of Public Highways, predecessor to the Ministry of Transportation of Ontario (MTO), assumed control of the Halton County road between Palermo (since amalgamated into a neighbourhood of Oakville) and Milton on April 14, 1925.

On April 25, the route was extended north by 10.0 km (6.2 mi) to Highway 24 in Ospringe.

[3] The following table lists the major junctions along Highway 25, as noted by the Ministry of Transportation of Ontario.