John William Hennessy (born March 12, 1955) was a professional American football player who played linebacker for three seasons for the New York Jets from 1977 to 1979. He appeared in 46 NFL games and was a starter at linebacker in all 16 regular season games for the 1978 New York Jets. He played college football at the University of Michigan from 1974 to 1976. In May 1980, Hennessy was claimed by the Green Bay Packers after being placed on waivers by the Jets. He was released the Packers in late July 1980.