William Kirby (September 19, 1759 – July 4, 1850) was an English entomologist.

Kirby was born at Witnesham in Suffolk, and studied at Ipswich grammar school and Caius College, Cambridge, where he graduated in 1781. Taking holy orders in 1782, he spent his entire life in the peaceful seclusion of an English country parsonage at Barham in Suffolk. His favorite study was natural history; and eventually entomology engrossed all his leisure. His first work of importance was his Monographia Apum Angliae (2 vols. 8vo, 1802), which as the first scientific treatise on its subject brought him into notice with the leading entomologists of his own and foreign countries. The practical result of a friendship formed in 1805 with William Spence, of Hull, was the jointly written Introduction to Entomology (4 vols., 1815-1826; 7th ed., 1856). In 1830 he was chosen to write one of the Bridgewater Treatises, his subject being The History, Habits, and Instincts of Animals (2 vols., 1835).

Besides the books already mentioned he was the author of many papers in the Transactions of the Linnean Society, the Zoological Journal and other periodicals; Strictures on Sir James Smith's Hypothesis respecting the Lilies of the Field of our Saviour and the Acanthus of Virgil (1819); Seven Sermons on our Lords Temptations (1829); and he wrote the sections on insects in the Account of the Animals seen by the late Northern Expedition while within the Arctic Circle (1821), and in Faunea Boreali-Americana (1837). His Life by the Rev. John Freeman , published in 1852, contains a list of his works.