Sir William Cornwallis (ca. 1579 – 1614) was an early English essayist.
His Essayes (pub. 1616) are written, unusually for the time, in the tradition of Montaigne, rather than that of Francis Bacon. He also wrote Essayes of Certaine Paradoxes (1617) containing the "Encomium on Richard III," and Discourses upon Seneca the Tragedian (1601), the first book in English on the drama of Seneca the Younger.