List of former Ontario provincial highways

The Canadian province of Ontario has an extensive network of Primary (King's), Secondary, and Tertiary Highways, with county-level and city-level roads linking between them.

In 1997 and 1998, many sections of the provincial highway network were downloaded to local municipalities (such as cities, counties or regional municipalities) by the Ontario Ministry of Transportation as a cost-saving measure.

While highways were occasionally transferred to local governments in the past, the 1997–1998 downloads represented the most significant changes to Ontario's highway network.

Many highways were completely devolved, while of others only short sections remain under provincial jurisdiction (Highway 2, once stretching across Southern Ontario, now is only a few kilometres long).

Highway numbers have even been "recycled" (used more than once on a provincial highway), however the use tends to be as far as possible from the original routing, and generally a few decades' time separate each numbering, to minimize confusion.