Underdown is a surname. Notable people with the surname include:
David Edward Underdown (David Underdown) (1925-2009), English historian
Charles Edward Underdown (Edward Underdown) (1908-1989), English actor
Emanuel Maguire Underdown (1831-1913), English barrister, author and industrialist
Emily Underdown (1863-1947), English author
Harry Charles Bailee Underdown (1877-1963), English barrister and industrialist
Thomas Underdown (16th century), English poet and translator
