John A. Hennessy (1859 - April 22, 1951), was a newspaper editor and a special investigator for Governor Sulzer in the Tammany Hall corruption trial of 1913.
He was a member of the New York State Assembly in 1893 (Kings Co., 8th D.), 1894 and 1895 (both Kings Co., 2nd D.).
He died on April 22, 1951, in Brooklyn.