Below is a list of counties in the Canadian province of
Ontario. The term "county" is only used for the geographical units in the populous southern part of the province. The sub-divisions in the thinly populated northern part of the province are called districts. This list has not taken into account some recent reorganization of county boundaries.
- Algoma District, Ontario[?]
- Brant County, Ontario[?]
- Bruce County, Ontario[?]
- Carleton County, Ontario[?]
- Cochrane District, Ontario[?]
- Dufferin County, Ontario[?]
- Dundas County, Ontario[?]
- Durham Regional Municipality, Ontario[?]
- Elgin County, Ontario[?]
- Essex County, Ontario
- Frontenac County, Ontario[?]
- Glengarry County, Ontario[?]
- Grenville County, Ontario[?]
- Grey County, Ontario[?]
- Haldimand-Norfolk Regional Municipality, Ontario[?]
- Haliburton County, Ontario[?]
- Halton Regional Municipality, Ontario[?]
- Hamilton Municipality, Ontario
- Hastings County, Ontario[?]
- Huron County, Ontario[?]
- Kenora District, Ontario[?]
- Kent County, Ontario[?]
- Lambton County, Ontario[?]
- Lanark County, Ontario[?]
- Leeds County, Ontario[?]
- Lennox and Addington County, Ontario[?]
- Lincoln County, Ontario[?]
- Manitoulin District, Ontario[?]
- Middlesex County, Ontario
- Muskoka Regional Municipality , Ontario[?]
- Niagara Regional Municipality, Ontario[?]
- Nipissing District, Ontario[?]
- Norfolk County, Ontario[?]
- Northumberland County, Ontario[?]
- Ontario County, Ontario[?]
- Ottawa Municipality, Ontario
- Oxford County, Ontario[?]
- Parry Sound District, Ontario[?]
- Peel Regional Municipality, Ontario[?]
- Perth County, Ontario[?]
- Peterborough County, Ontario[?]
- Prescott County, Ontario[?]
- Prince Edward County, Ontario[?]
- Rainy River District, Ontario[?]
- Renfrew County, Ontario[?]
- Russell County, Ontario[?]
- Simcoe County, Ontario[?]
- Stormont County, Ontario[?]
- Sudbury District, Ontario[?]
- Sudbury Regional Municipality, Ontario[?]
- Thunder Bay District, Ontario[?]
- Timiskaming District, Ontario[?]
- Toronto Municipality, Ontario
- Victoria County, Ontario[?]
- Waterloo Regional Municipality, Ontario
- Welland County, Ontario[?]
- Wellington County, Ontario[?]
- Wentworth County, Ontario[?]
- York Regional Municipality, Ontario