Diemer is a surname. Notable people with the surname include:
Brian Diemer (born 1961), American middle distance runnerEmil Josef Diemer (1908–1990), German chess playerEmma Lou Diemer (born 1927), American composerFranz-Zeno Diemer (1889–1954), German aviatorHugo Diemer (1870–1937), American engineer, consultant, professor and management authorJohann Heinrich Diemer (1904–1945), Dutch biologistKurt Diemer (1893–1953), German footballerLouis Diémer (1843–1919), French classical pianist and composerMarv Diemer (1924–2013), American politician and businessmanWalter Diemer (1904–1998), American inventor