The First Meeting of the Executive Council of Upper Canada
Because of the Loyalist influx into the western part of Quebec after the American Revolution, the province was divided into Upper and Lower Canada (now Ontario and Quebec). The Constitutional Act of 1791 provided for representative government in each of the new provinces. On July 8, 1792, John Graves Simcoe, Lieutenant Governor of Upper Canada, met his Executive Council in St. George's Church which one occupied this site. In the following three weeks the Council divided the province into counties and allocated representation to the Assembly that was to meet at Newark (later Niagara-on-the-Lake) in September.
Plaque via Alan L. Brown's site Ontario Plaques. Full page here.