List of census divisions of Ontario

First-level administrative divisions of Ontario
First-level administrative divisions of Ontario
Location	Province of Ontario
Number	51
Populations	13,255 (Manitoulin District) – 2,731,571 (City of Toronto)
Areas	630.20 km2 (City of Toronto) – 407,268.65 km2 (Kenora District)

The Province of Ontario has 51 first-level administrative divisions, which collectively cover the whole province. With two exceptions,^[a] their areas match the 49 census divisions Statistics Canada has for Ontario.

The Province has four types of first-level division: single-tier municipalities, regional municipalities, counties, and districts. The first three are types of municipal government but districts are not—they are defined geographic areas (some quite large) used in many contexts. The last three have within them multiple smaller, lower-tier municipalities but the single-tier municipalities do not. Regional municipalities and counties differ primarily in the services that they provide to their residents. (Lower-tier municipalities are generally treated as census subdivisions by Statistics Canada.)

In some cases, an administrative division may retain its historical name even if it changes government type. For instance, Oxford County, Haldimand County, Norfolk County and Prince Edward County are no longer counties: Oxford is a regional municipality and the others are single-tier municipalities. Several administrative divisions in Ontario have significantly changed their borders or have been discontinued entirely. See: Historic counties of Ontario.
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[a]