The Reverand William Darwin Fox (1805-1880) was an English clergyman, naturalist and cousin of Charles Darwin.

Fox was the son of Samuel Fox (1765 — 1851), and Anne Darwin, the daughter of Robert Darwin, and sister of Erasmus Darwin.

Like Charles Darwin, Fox prepared for the clergy at Cambridge University. He was also a naturalist and entomologist, particularly collecting beetles. At Cambridge, Fox and Darwin became friends, and Fox tutored his younger cousin on natural history. Fox graduated from Cambridge in the winter of 1829 and Rector of Delamere, Cheshire, 1838–1873. He then retired to Sandon on the Isle of Wight, and is buried there.

Fox married twice and had sixteen children. His first wife was Harriet Fletcher, (1799–1842), daughter of Sir Richard Fletcher whom he married in 1834 and they issued Samuel William Darwin Fox, (b. 1841), a clergyman, Harriet Emma Fox (no date), Robert Gerard Fox JP ( b. 1849).

His second wife was Ellen Sophia (1820–1887), daughter of Basil George Woodd of Hillfield, Hampstead in 1846. They issued Theodora Fox, 1853–78, Frederick William Fox, b. 1855, Gilbert Basil Fox, b. 1864, Louisa Mary Fox, 1850–1853,