In 1791 Simcoe was appointed LIEUTENANT-GOVERNOR of Upper Canada [Ontario]. He arrived in June 1792 after wintering at Quebec. He governed UPPER CANADA until 1796. This was a daunting task, for he had to create a functioning colony, with all the framework of government, in a sparsely populated land of thick forest. In all Upper Canada there were barely 10 000 settlers. They were mainly recently arrived Loyalists and most of them lived in the eastern part of the colony along the lakes and rivers that served as highways. Simcoe established his first capital city at the small settlement of Newark [Niagara-on-the-Lake]. But this was dangerously near the American border. Simcoe would have preferred to establish his capital at what he called New London, on the Thames River, but he lacked the resources at that time. Meanwhile, in 1793, he began to build a temporary capital, York, on the northwest shore of Lake Ontario. This was the nucleus of today's TORONTO.

To get the country settled quickly, Simcoe gave large grants of land to prominent Loyalists and to anyone else who promised to organize settlement. He also advertised for settlers in the United States. So many Americans took up his offer that by 1812 about 60% of the population were American-born non-Loyalists. Meanwhile, Simcoe had roads cut through the forest. A major route was Yonge Street, which was begun in 1793 and ran from York to Lake Simcoe by 1796.

Simcoe went on to be governor of Santo Domingo in the Caribbean (1797) and later of the Western District of England. He was appointed Commander in Chief for India in 1806 but died before he could take up the position.