London was named for the British capital of London by John Graves Simcoe, who also named the local river the Thames, in 1793. Simcoe had intended London to be the capital of Upper Canada. Guy Carleton (Governor Dorchester) rejected that plan after the War of 1812, but accepted Simcoe's second choice, the present site of Toronto, to become the capital city of what would become the Province of Ontario, at Confederation, on 1 July 1867.
