Sir William Acton, 1st Baronet (1570 – 22 January 1651) was an English merchant and Royalist who was Lord Mayor of London in 1640. Acton was the son of Richard Acton, a London merchant, and Margaret Daniel. He was apprenticed by the Merchant Taylor Company in 1593 and freed in 1601. On 12 February 1628, he was elected an alderman of the City of London for Aldersgate ward. That same year, he was Sheriff of London. He was created a baronet on 30 May 1629.