List of Ontario census divisions

Below is a list of census divisions in the Canadian province of Ontario. A census division in Canada can be defined as a provincially legislated area, such as a county or regional municipality. They are the intermediate geographic areas between the province level and the municipality (census subdivision).

These can be divided into single-tier and upper-tier municipalities.

Single-tier municipalities are standalone cities and municipalities where there is only one level of municipal government in an area.

Upper-tier municipalities are agglomerations of lower-tier municipalities, such as towns and townships, where it is legislated or more efficient to provide certain services, such as water, electricity, and police coverage, over an area that includes more than one municipality. In Ontario, these include:

counties, which are small governments with townships and cities within them;
regional municipalities, which also have smaller divisions within them, but are larger governments with more responsibility; and
the District Municipality of Muskoka, which is the only district in Ontario that provides regional-scale services

A number of the cities and regions were once counties, or part of counties; see Historic counties of Ontario.

In Northern Ontario, the term district is used to denote regional areas, but these are simply territorial boundaries that do not serve any municipal government purpose. Many of these districts are comprised primarily of unincorporated lands. Some districts may have District Social Service Administration Boards, which are designed to provide certain social services, but they do not serve a governmental function.

These divisions, among others, are used by Statistics Canada to aggregate census data.