St. Thomas Orthodox Church in Sioux City, Iowa is a parish of the Great Plains Deanery of the Diocese of Wichita and Mid-America, part of the Antiochian Orthodox Christian Archdiocese of North America, a constituent archdiocese of the Greek Orthodox Patriarchate of Antioch and All the East. Founded in 1916 to serve the Syrian and Lebanese immigrant community that existed in Sioux City at that time, it is the oldest Orthodox parish in Sioux City and has become a pan-Orthodox community with members from across the Siouxland region.