C
- C.J. Allen, British sculptor
- Carl Meredith Allen (accused), source of the Philadelphia Experiment story
- Charles Allen, several people
- Charles Peter Allen (1861–1930), English politician
- Charlie Allen, several people
- Chris Allen, several people
- Christian Allen, video game designer
- Christopher Allen (born 1944), former English cricketer
- Clarence Allen (geologist), member of the National Academy of Sciences
- Clarence Emir Allen (1852–1932), U.S. Representative from Utah
- Clarence Ray Allen (1930–2006), American prison inmate who was executed by lethal injection
- Clive Allen (born 1961), English footballer
- Clive Allen (basketball) (born 1961), English basketball player
- Corey Allen (born 1934), American film and television director, producer, writer and actor
- Craig Allen (footballer), former footballer from Guernsey
- Craig Allen (meteorologist) (born 1957), American meteorologist
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