Shannon City is a city in southern Union and northern Ringgold counties in the U.S. state of Iowa. The population was 73 at the time of the 2020 …Shannon City is a city in southern Union and northern Ringgold counties in the U.S. state of Iowa. The population was 73 at the time of the 2020 census. Shannon City is two miles west of US Route 169 along the Union-Ringgold County line. The Grand River flows past the southeast side of the community.