Named for Sir Robert Peel, Prime Minister of the United Kingdom, the county was organized in 1851.

The Credit River was reserved for the Mississaugas; however, they sold their land and moved to the Bruce Peninsula.

[2] It was given its own provisional county council in 1856,[3] and was formally separated from York in 1860.

[4] However, disputes as to whether the county seat should be Malton or Brampton[5] prompted the provisional council to request that the separation be reversed, and an 1862 Act of the Parliament of the Province of Canada brought that into effect, reviving the United Counties of York and Peel.

[7] In 1973, Peel County became the Regional Municipality of Peel, as a result of the Ontario provincial government's regionalization of the rapidly developing counties surrounding Toronto.