Farnum is a surname that may refer to:

• Billie S. Farnum (1916–1979), U.S. Representative and labor leader from Michigan
• Dorothy Farnum (1900–1970), American screenwriter
• Dustin Farnum (1874–1929), American singer, dancer and silent movie actor
• E. B. Farnum (1826–?), first mayor of Deadwood, South Dakota
• Fay Farnum (1888–1977), American mathematician
• Franklyn Farnum (1878–1961), American character actor
• Herbert Cyrus Farnum (1866–1926), American landscape painter
• John Egbert Farnum (1824–1870), United States Army brevet brigadier general of volunteers
• Kenneth Farnum (born 1931), Jamaican cyclist who competed in the 1952 Olympics
• Mark Farnum (c. 1896–1957), All-American college football player
• Marshall Farnum (1879–1917), American actor and film director
• Royal B. Farnum (1884–1967), American art educator and President of the Rochester Institute of Technology
• William Farnum (1876–1953), Hollywood film actor