The first Monday in August is a holiday all across Ontario. But the holiday is called different things in different areas.
In fact, the first Monday in August is a municipal holiday. The Civic Holiday is not designated as an official statutory holiday by provincial legislation. In the past few years, a number of private member's bills have been introduced in the Ontario Legislature attempting to make it official, but none has passed to date.
The concept of a midsummer holiday in Toronto dates as far back as 1869. In Toronto today, the holiday is celebrated as “Simcoe Day”, but according to recent studies, only 16% of the population actually knows that. While other Ontario municipalities have chosen to honour a significant local person or organization to help focus the celebration (see a selection in the chronology below), in most municipalities the day is referred to as the “August Civic Holiday”. Source.