Ontario counties have had varied histories. A number of counties, suchas Ontario County and Toronto County, have long ago disappeared as theprovince grew. Through past redistribution schemes some were amalgamatedwhile others gave up territory which became distinctly separate counties.For example, Wellington County gave rise to parts of Dufferin. That happenedover one hundred years ago, but even today, Dufferin and Wellington sharemany services. Such redistribution and amalgamation still goes on eventoday

Along with county sub-divisions, the province also has administrativedistricts, hence the name of this category is Counties and Districts. ParrySound District is an example of a district. .

At the time of this writing, Ontario had 39 remaining county or districtsub-divisions. Through more recent reorganization and in a few instancesof amalgamation, a number of Ontario counties became the parents of neweradministrative areas known as Regional Municipalities. For example, TheRegional Municipality of York has its roots in York County, while The RegionalMunicipality of Waterloo is the end product of Waterloo County. In a fewcases, counties were combined or united as in the case of Stormont, Dundasand Glengarry Counties are considered a single united administrative district.

The names of such recently altered counties remain in this categoryfor historical reference. The changes are recent occurences, and many peoplestill think in terms of the original county, rather than the newer locality,or maybe even of both. Still they are linked directly to the newer locality.

The following list includes counties which no longer exist in their originalform, but instead in a Regional Municicpality, or other context. They are the Counties of Dundas, Durhham, Glengarry, Haldimand, Halton,Kent, Lincoln, Peel, Victoria, Waterloo, Welland, Wentworth and York.