Underdown is a surname. Notable people with the surname include:Charles Edward Underdown (1908–1989), English actor David Underdown (1925–2009), English historian Emanuel Maguire Underdown (1831–1913), English barrister, author and industrialist Emily Underdown (1863–1947), English author George Underdown (1859–1895), English cricketer Harry Charles Bailee Underdown (1877–1963), English barrister and industrialist James Underdown, executive director of The Center for Inquiry (CFI) West in Los Angeles Thomas Underdown, English poet and translator