John Graves Simcoe (25 February 1752 – 26 October 1806) was a British Army general and the first Lieutenant Governor of Upper Canada from 1791 until 1796 in southern Ontario and the watersheds of Georgian Bay and Lake Superior. He founded York (now Toronto) and was instrumental in introducing institutions such as courts of law, trial by jury, English Common law, and freehold land tenure, and also in the abolition of slavery in Canada.

Simcoe was the only surviving son of John (1710–1759) and Katherine Simcoe (d. 1767). His parents had four children, but he was the only one to live past childhood; Percy drowned in 1764, while Paulet william and John william died as infants. His father was a captain in the Royal Navy who commanded the 60-gun HMS Pembroke during the Siege of Louisbourg (1758), with James Cook as his sailing master. He died of pneumonia on 15 May 1759 on board his ship in the mouth of the Saint Lawrence River, a few months prior to the siege of Quebec. The family then moved to his mother's parental home in Exeter. His paternal grandparents were william and Mary (née Hutchinson) Simcoe.

He was educated at Exeter Grammar School and Eton College. He spent a year at Merton College, Oxford; he was then admitted to Lincoln's Inn, but decided to follow the military career for which his father had intended him. He was initiated into Freemasonry in Union Lodge, Exeter on 2 November 1773.

Simcoe wrote a book on his experiences with the Queen's Rangers, titled A Journal of the Operations of the Queen's Rangers from the end of the year 1777 to the conclusion of the late American War, which was published in 1787.

On August 31, 1778, Lieut. Col. Simcoe led a massacre of forty Native Americans, allied with the Continental Army, in what is today the Bronx, NY. This place is known as Indian Field in Van Cortlandt Park, Bronx. NY.

During October 1779, Simcoe and 80 men launched an attack on central New Jersey from southern Staten Island known as Simcoe's Raid, from what is known today as the Conference House, resulting in the burning of Patriot supplies inside a Dutch Reformed Church in Finderne, including hay and grain; the release of Loyalist prisoners from the Somerset County Courthouse; and Simcoe's capture by Armand Tuffin de La Rouërie. Simcoe was released at the end of 1779 and rejoined his unit in Virginia. He was involved in a skirmish near Williamsburg and was at the Siege of Yorktown. He was invalided back to England in December of that year as a Lieutenant-Colonel, having been promoted in March 1782.

Simcoe convalesced at the Devon home of his godfather, Admiral Samuel Graves. In 1782, Simcoe married Elizabeth Posthuma Gwillim, his godfather's ward. Elizabeth was a wealthy heiress, who acquired a 5,000 acre estate at Honiton in Devon and built Wolford Lodge. Wolford was the Simcoe family seat until 1923.

Simcoe's first priority was the North West Indian War between the United States and the "Western Confederacy" of Native Americans west of the Appalachian Mountains and south of the Great Lakes (the Shawnee, Miami, Wyandot, and other tribes). This conflict had begun in 1785, and was still raging when Simcoe arrived in 1792. Simcoe had hoped to form an Indian buffer state between the two countries, even though he distrusted Joseph Brant, the main Indian leader. Simcoe rejected the section of the Treaty of Paris (1783) which awarded that area to the US, on the grounds that American actions had nullified the treaty. However, the French Revolutionary Wars broke out in 1793. The government in London decided to seek good terms with the United States. Simcoe was instructed to avoid giving the US reason to mistrust Britain but, at the same time, to keep the Native Americans on both sides of the border friendly to Britain. The Indians asked for British military support, which was initially refused, but in 1794 Britain supplied the Indians with rifles and ammunition.

Simcoe entered politics in 1790. He was elected Member of Parliament for St Mawes in Cornwall, as a supporter of the government (led by william Pitt the Younger). As MP, he proposed raising a militia force like the Queen's Rangers. He also proposed to lead an invasion of Spain. But instead he was to be made lieutenant governor of the new loyalist province of Upper Canada. He resigned from Parliament in 1792 on taking up his new post.

Simcoe was appointed Lieutenant-Governor on 12 September 1791, and left for Canada with his wife Elizabeth and daughter Sophia, leaving three daughters behind in England with their aunt. They left England in September and arrived in Canada on 11 November. Due to severe weather, the Simcoes spent the winter in Quebec City. Simcoe finally reached Kingston, Upper Canada on 24 June 1792.

Under the Constitutional Act, the provincial government consisted of the Lieutenant-Governor, an appointed Executive Council and Legislative Council, and an elected Legislative Assembly. The first meeting of the nine-member Legislative Council and sixteen-member Legislative Assembly took place at Newark (now Niagara-on-the-Lake) on 17 September 1792.

Simcoe began construction of two roads through Upper Canada, for defence and to encourage settlement and trade. Yonge Street (named after British Minister of War Sir George Yonge) ran north-south from York to Lake Simcoe. Soldiers of the Queen's Rangers began cutting the road in August 1793, reaching Holland Landing in 1796. Dundas Street (named for Colonial Secretary Henry Dundas) ran east-west, between York and London.

In 1794 Simcoe had been appointed Major-General. In July 1796 poor health forced him to return to Britain. He was unable to return to Upper Canada and resigned his office in 1798.

He served briefly as the commander of British forces in Saint-Domingue (later Haiti). There, in the spring of 1797, he defended the coastal town of Saint-Marc but lost Mirebalais and the Central Plateau to the forces of Toussaint Louverture, leader of the slave revolt and by that point commander-in-chief of the French Republican forces on the island. This campaign signalled the end of the English attempt, in collaboration with planters, to restore slavery and other aspects of the ancien regime to take over the rich, sugar-producing island while France was involved in internal affairs of its Revolution.

Simcoe was appointed colonel of the 81st Foot in 1798, but exchanged the position for the 22nd Foot less than six months later. He was also promoted to Lieutenant-General and was made commander of the Western District. In 1806, he was appointed Commander-in-Chief, India (to succeed Cornwallis, who had died shortly after arriving in India.) Simcoe died in Exeter before assuming the post. Gerard Lake, 1st Viscount Lake, was reappointed to replace Simcoe.

Slavery was thus ended in Upper Canada long before it was abolished in the British Empire as a whole. By 1810, there were no slaves in Upper Canada, but the Crown did not abolish slavery throughout the Empire until 1834.

Captain John Kennaway Simcoe, the last member of the Simcoe family, died without issue in 1891 and was survived by widow beyond 1911.

Simcoe was buried in Wolford Chapel on the Simcoe family estate near Honiton, Devon. The Ontario Heritage Foundation acquired title to the chapel in 1982.

Simcoe realised that Newark made an unsuitable capital because it was on the Canada–US border and subject to attack. He proposed moving the capital to a more defensible position, in the middle of Upper Canada's southwestern peninsula between Lake Erie and Lake Huron. He named the new location London, and renamed the river there the Thames in anticipation of the change. Dorchester rejected this proposal, but accepted Simcoe's second choice, the present site of Toronto. Simcoe moved the capital there in 1793, and renamed the settlement York after Frederick, Duke of York, King George III's second son. The town was severely underdeveloped at the time of its founding so he brought with him politicians, builders, Nova Scotia timber men, and Englishmen skilled in whipsawing and cutting joists and rafters.