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. Over the years, however, Ontario has turned back numerous highways to municipal government bodies, renumbered them, or upgraded them to 400-series highways.

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). Below is a partial list of partially or wholly devolved highways since 1997.