The following summarizes MISA Ontario's four administrative regions:

Northern Region
Includes the municipal governments of and within:

• Districts: Algoma, Cochrane, Kenora, Manitoulin, Muskoka, Nipissing, Parry Sound, Rainy River, Sudbury, Thunder Bay, and Timiskaming.
• Single Tier Municipality: City of Greater Sudbury.

Eastern Region
Includes the municipal governments of and within:

• Counties: Frontenac, Hastings, Lanark, Leeds & Grenville, Lennox & Addington, Prescott & Russell, Renfrew, Stormont, Dundas and Glengarry;
• Single Tier Municipalities: City of Ottawa, County of Prince Edward

Central Region
Includes the municipal governments of and within:

• Counties: Haliburton, Northumberland, Peterborough. Simcoe.
• District: Haliburton.
• Regions: Durham; Halton; Peel; York.
• Single Tier Municipalities: City of Toronto, City of Kawartha Lakes.

Western Region
Includes the municipal governments of and within:

• Counties: Brant, Bruce, Dufferin, Elgin, Essex, Grey, Huron, Lambton, Middlesex, Norfolk, Oxford, Perth, Wellington
• Regions: Niagara, Waterloo.
• Single Tier Municipalities: County of Brant, City of Brantford, Municipality of Chatham-Kent, County of Haldimand, City of Hamilton.