Ontario County was the name of two historic counties in the Canadian province of Ontario.Ontario County (1792-1800)The original Ontario County existed from 1792 to 1800 as part of the Eastern District, and consisted of the islands in the St. Lawrence River. After 1800, Ontario County was dissolved and the islands were reassigned to the nearest mainland counties:Lennox and AddingtonHastingsPrince Edward Leeds County and Grenville CountyStormont, Dundas and Glengarry
