William Cookworthy (11 April 1705 - 17 October 1780) was a chemist and Quaker from Kingsbridge, Devon. He discovered china clay in Cornwall and devised a way of making porcelain, which previously had had to be imported from China. He was also an associate of John Smeaton, who lodged at his house when he was engaged in building the third Eddystone Lighthouse (1756-1759). Cookworthy helped Smeaton with the development of hydraulic lime , which was essential to the successful building of the lighthouse.