Diemer is a surname. Notable people with the surname include:
Arts and entertainment Emma Lou Diemer (1927–2024), American composer Louis Diémer (1843–1919), French classical pianist and composer Michael Zeno Diemer (1867–1939), German painter
Sports and pastimes Brian Diemer (born 1961), American middle distance runner Emil Josef Diemer (1908–1990), German chess player Kurt Diemer (1893–1953), German footballer
Other Franz-Zeno Diemer (1889–1954), German aviator Helen Diemer, American architectural lighting designer Hugo Diemer (1870–1937), American engineer, consultant, professor, and management author Johann Heinrich Diemer (1904–1945), Dutch biologist Marv Diemer (1924–2013), American politician and businessman Walter Diemer (1904–1998), American inventor