Navy Island
The British used Navy Island from 1761 to 1764 as a shipyard in which to build the first British decked vessels to sail the upper lakes. These were essential in maintaining the supply lines westward during Pontiac's uprising, 1763-4. Thereafter the island remained undisturbed until 14 December 1837 when William Lyon Mackenzie, after being defeated at Toronto, led a "Patriot" army from Buffalo to occupy it. Swift reaction by local militia and British regulars prevented his moving to the mainland and on 14 January 1838, facing a hopeless situation, he abandoned the island.
Plaque via Alan L. Brown's site Ontario Plaques. Full page here.