Sir William Thorold, 1st Baronet (1591–1678) was an English landowner and politician who sat in the House of Commons from 1661 to 1677.
Thorold was the second son of William Thorold, of Marston, Lincolnshire and his wife Frances, daughter of Sir Robert Tyrwhitt, of Kettleby, Lincolnshire.
He succeeded his elder brother Anthony Thorold.
He was Sheriff of Lincolnshire from 1632 to 1633 and was created baronet of Marston on 24 August 1642.
In the Civil War, he fought for the King and suffered greatly as a result.