Johnson, Sir William (1715–74), superintendent of Indian affairs in colonial America (specifically among the Iroquois and their allies in New York), was born at Smithtown, Co. Meath, one of seven children (three sons and four daughters) of Christopher Johnson, tenant farmer, and Anne Johnson (née Warren). The Johnsons claimed to be a ‘line honorable in its alliances’: both the Johnsons and Warrens conformed to the Church of Ireland, probably during the early eighteenth century.
In early 1738 Johnson arrived in America to oversee the Mohawk valley estate of his uncle, Vice-admiral Sir Peter Warren, at Warrensburg, New York, near the mouth of the Schoharie river and covering twenty-two square miles (57sq.km). By 1740 he had built his own home, Mount Johnson, across the river from Warrensburg. To run the household he chose a German indentured servant, Catherine Weisenberg, who became the mother of three of his children: a son, Sir John Johnson (who became a loyalist leader in the American revolution, later settling in Canada), and two daughters, Ann (‘Nancy’) and Mary. For the farm he recruited twelve families in Co. Meath and also brought along as a companion his cousin, Michael Tyrrell, who later grew tired of frontier life and gained a naval commission through Peter Warren's aid. This began a pattern (which Johnson followed throughout his career) of settling Irish immigrants on his estates, as well as Palatine Germans: these served as a buffer against the often antagonistic Albany Dutch, who had long held a virtual monopoly on trade with the Iroquois and also carried on an illegal trade with the French and native peoples in Canada.
During this period, Johnson began trading with the Six Nations (Iroquois confederacy), as well as supplying the settlers in the Mohawk valley. His close relationship with the Six Nations, particularly the Mohawks, led him into the political and military arenas, influencing his ideas of how the colonies should manage questions of trade and westward expansion. By 1745–8, when he participated in the war of the Austrian succession (called ‘King George's war’ in North America), he had already gained the confidence of Tiyanoga, a Mohawk sachem (administrative chief), known to the Dutch as ‘King Hendrick’, who had travelled to England in 1709–10 and again in 1740. Johnson's friendship with the Mohawks was so great that he was adopted into the tribe and renamed Warraghiyagey (‘Chief Big Business’ or ‘Doer of great things’). Johnson learned the Mohawk language, and he also adopted their clothing and customs when among them.
In 1746 the New York assembly voted to provide Johnson with funds to supply Fort Oswego on Lake Ontario and he was named ‘colonel of the … Six Nations and commissary for Indian affairs’ by the royal governor of New York, George Clinton (son of Irishman George Clinton). Returning to the Mohawk valley following the end of the war, in 1748 Johnson began building Fort Johnson, a stone house still in existence. Johnson participated in the Albany congress (1754) which helped formulate British policy toward native peoples. In April 1755 the crown confirmed Johnson as superintendent of Indian affairs with full powers to treat with the Six Nations and their allies, and he was also commissioned major-general by the northern colonial governments.
Increasing French encroachments on the north-western frontier eventually led to the Seven Years' War (officially 1756–63, though it began and ended earlier in North America, where it is called ‘the French and Indian war’). Although Johnson's expedition to capture the French fort at Crown Point failed, he soundly defeated the French under Baron Dieskau at Lake George (September 1755) and later established Forts Edward and William Henry. In November 1755 the king made him a baronet (only the second in the American colonies). He participated in the siege of Niagara (1759), which fell to him on 25 July, and in 1760 he served with General Jeffery Amherst in the capture of Montreal. That year the Mohawks bestowed the title of sachem on him. In 1761 he journeyed to Detroit, part of a diplomatic mission to pacify the Native Americans of that region. In 1762 he founded Johnstown, New York, where he established his principal residence.
After Catherine Weisenberg's death (1759), Mary (‘Molly’) Brant, daughter of the sachem Nichuls Brant (Aroghyiadecker) and sister of Joseph Brant, the Mohawk leader during the American revolution, came to manage the household, first at Fort Johnson and later at the Georgian-style Johnson Hall, built in 1763, still in existence. Between 1759 and 1773 she bore William nine children, of whom eight survived, two sons and six daughters. One son, Peter Johnson, was killed aged seventeen fighting on the British side during the American revolution, and Molly (known also as Degonwadonti) herself led Mohawk warriors. After that war, Molly and her family settled in Kingston, Ontario, where she died in 1796, about sixty years old. Sir William Johnson had died on 11 July 1774, aged fifty-nine, probably from cirrhosis of the liver, undoubtedly a result of years of hard drinking and entertaining Native Americans and Europeans at Fort Johnson and Johnson Hall, which were renowned centres of hospitality in the Mohawk valley.
Portraits of Johnson may be found in the Public Archives of Canada, Albany Institute of History and Art, New York Historical Society, and Derby Museum and Art Gallery (the last, by Benjamin West, showing him rescuing a French officer from a tomahawk-wielding Iroquois). His papers were edited by the New York State Division of Archives, Albany (13 vols, 1921–62).