James Smithson was born in c. 1765 to Hugh Percy, 1st Duke of Northumberland and Elizabeth Hungerford Keate Macie. His mother was the widow of John Macie, a wealthy man from Weston, Bath. An illegitimate child, Smithson was born in secret in Paris, resulting in his birth name being the Francophone Jacques-Louis Macie (later altered to James Louis Macie). In 1801 when he was about 36, after the death of his again-widowed mother, he changed his last name to Smithson, the original surname of his biological father. (Baronet Hugh Smithson had changed his surname to Percy when he married Lady Elizabeth Seymour, already a baroness and indirect heiress of the Percy family, one of the leading landowning families of England).