Delong or DeLong is a surname. Notable people with the surname include:
Alana DeLong, Canadian politician
Delmar DeLong, American politician
Ding Delong, military officer
Gary DeLong, American soccer player
George W. DeLong (1844–1881), United States Navy officer and explorer
J. Bradford DeLong (born 1960), economist
Jesse Delong (1805–1868), Canadian politician
Jia Delong (born 1985), baseball player
Joe DeLong (born 1972), American (West Virginian) politician
Keith DeLong (born 1967), football player
Mahlon DeLong, American neurologist
Michael Delong, American military officer
Richard DeLong, Sacred Harp singing
Russell V. DeLong (1901–1981), minister and college president
Sidney Randolph DeLong (1875–1914), American politician
Solomon DeLong (1849–1925), writer and journalist
Sophie Delong (born 1957), French politician
Steve DeLong (1943–2010), American football player