Sir William Johnson, 1st Baronet (1715 – 11 July 1774), founder of Johnstown, New York, was an Irish pioneer and army officer in colonial New York, and the British Superintendent of Indian Affairs from 1755 to 1774. He served on the Governor's Council in New York, earned the rank of Major General in the British forces during the French and Indian War. His contributions in that war earned him a baronetcy and enormous land grants in the Mohawk Valley. Sir William was a man of many accomplishments who created the city of Johnstown. His estate in the Mohawk River Valley covered over 400,000 acres (1,600 km²).

William Johnson was born to Christopher Johnson - son of William MacShane and great, great grandson of Sir Turlough mac Henry Ó Néill - in County Meath, Ireland in 1715. The family was originally the O'Neills of the Fews in Armagh and thus a branch of the Uí Néill, but had been dispossessed by the Irish Confederate Wars and the Williamite war in Ireland. William's father was originally known as William MacShane (Ó Néill) but changed his name to the English version of MacShane: Johnson.

William Johnson is thought to have originally planned a mercantile or legal career, but in 1737 he emigrated to America to manage and settle a large tract of land granted to his uncle, Admiral Sir Peter Warren. This area was known as Warrensburg. On June 30, 1739 Johnson bought a tract of land in New York in his own name, 1/4 mile long and one mile (1.6 km) deep for £180 on the north side of the Mohawk River, a house and small farm. Later he built a stone mansion which he referred to as 'Mount Johnson'. After the outbreak of the French and Indian War, 'Mount Johnson' became known as 'Fort Johnson', a defence post to which Johnson added two blockhouses by the 1750s.