The Canadian province of Ontario has several historic counties, which are past census divisions that no longer exist today. Most historic counties either merged with other counties, or became regional municipalities or single-tier municipalities. Although counties had existed prior to 1849, after 1849 they replaced the district systems in administering local government and courts in Ontario.
The county system is used in southern, southwestern and eastern sections of the province of Ontario. There are no counties in Northern Ontario due to sparse population and a long-standing boundary dispute with the Northwest Territories (that was not resolved until 1912).