Magnolia is a city in Harrison County, Iowa, United States. The population was 190 at the time of the 2020 census. Harrison County was establiā¦Magnolia is a city in Harrison County, Iowa, United States. The population was 190 at the time of the 2020 census. Harrison County was established in 1851 and organized on March 7, 1853. Abram Fletcher, Charles Wolcott and A. D. Jones were appointed by the Iowa General Assembly as Commissioners to organize the county and establish a county seat. They chose the location for Magnolia and gave it its name. The third building that was erected in the town for the county courthouse in 1873 was listed on the National Register of Historic Places. The building was demolished in 2019 due to extreme disrepair and the lack of funds to maintain it.