Sir William Cubitt (1785–1861) was an eminent English civil engineer and millwright. Born in Norfolk, England, he was employed in many of the great engineering undertakings of his time. He invented a type of windmill sail and the prison treadwheel, and was employed as chief engineer, at Ransomes of Ipswich, before moving to London. He worked on canals, docks, and railways, including the South Eastern Railway and the Great Northern Railway.