Henry St. John (July 16, 1783–1869) was a U.S. Representative from Ohio.
Born in Washington County, Vermont, St. John received a limited schooling. He served during the War of 1812. He moved to Wooster, Ohio, in 1815, to Crawford County, Ohio, in 1828, and in 1837 to Seneca County, where he engaged in agricultural pursuits, milling, and storekeeping near Tiffin, Ohio.
St. John was elected as a Democrat to the Twenty-eighth and Twenty-ninth Congresses (March 4, 1843-March 3, 1847). He was not a candidate for renomination. He resumed agricultural pursuits. Resided in Tiffin, Ohio, where he died in May 1869.