Adair County (1851 - Present)
Adams County (1851 - Present)
Allamakee County (1847 - Present)
Appanoose County (1843 - Present)
Audubon County (1851 - Present)
Bancroft County (1851 - 1855)
Belknap County Proposed (1874 - 1874)
Benton County (1837 - Present)
Black Hawk County (1843 - Present)
Boone County (1846 - Present)
Bremer County (1851 - Present)
Buchanan County (1837 - Present)
Buena Vista County (1851 - Present)
Buncombe County (1851 - Present)
Butler County (1851 - Present)
Carroll County (1851 - Present)
Cass County (1851 - Present)
Cedar County (1837 - Present)
Cerro Gordo County (1851 - Present)
Cherokee County (1851 - Present)
Chickasaw County (1851 - Present)
Clarke County (1846 - Present)
Clay County (1851 - Present)
Clayton County (1837 - Present)
Clinton County (1837 - Present)
Cook County (1836 - 1838)
Crawford County (1851 - Present)
Crocker County (1870 - 1871)
Dallas County (1846 - Present)
Davis County (1843 - Present)
Decatur County (1846 - Present)
Delaware County (1837 - Present)
Des Moines County (1834 - Present)
Dickinson County (1851 - Present)
Dubuque County (1834 - Present)
Emmet County (1851 - Present)
Fayette County (1837 - Present)
Floyd County (1851 - Present)
Fox County (1851 - Present)
Franklin County (1851 - Present)
Fremont County (1847 - Present)
Greene County (1851 - Present)
Grimes County Proposed (1876 - 1876)
Grundy County (1851 - Present)
Guthrie County (1851 - Present)
Hamilton County (1857 - Present)
Hancock County (1851 - Present)
Hardin County (1851 - Present)
Harrison County (1851 - Present)
Henry County (1836 - Present)
Howard County (1851 - Present)
Humboldt County (1851 - Present)
Ida County (1851 - Present)
Iowa County (1843 - Present)
Jackson County (1837 - Present)
Jasper County (1846 - Present)
Jefferson County (1839 - Present)
Johnson County (1837 - Present)
Jones County (1837 - Present)
Keokuk County (1837 - Present)
Kishkekosh County (1843 - Present)
Kossuth County (1851 - Present)
Larrabee County Proposed (1913 - 1913)
Lee County (1836 - Present)
Linn County (1837 - Present)
Louisa County (1836 - Present)
Lucas County (1846 - Present)
Madison County (1846 - Present)
Madison County Proposed (1844 - 1844)
Mahaska County (1843 - Present)
Marion County (1845 - Present)
Marshall County (1846 - Present)
Mills County (1851 - Present)
Mitchell County (1851 - Present)
Monona County (1851 - Present)
Montgomery County (1851 - Present)
Muscatine County (1836 - Present)
OBrien County (1851 - Present)
Osceola County (1851 - Present)
Page County (1847 - Present)
Palo Alto County (1851 - Present)
Plymouth County (1851 - Present)
Pocahontas County (1851 - Present)
Polk County (1846 - Present)
Pottawattamie County (1847 - Present)
Poweshiek County (1843 - Present)
Ringgold County (1847 - Present)
Risley County (1853 - Present)
Sac County (1851 - Present)
Scott County (1837 - Present)
Shelby County (1851 - Present)
Sioux County (1851 - Present)
Slaughter County (1838 - Present)
Story County (1846 - Present)
Tama County (1843 - Present)
Taylor County (1847 - Present)
Union County (1851 - Present)
Van Buren County (1836 - Present)
Wahkaw County (1851 - Present)
Wapello County (1843 - Present)
Warren County (1846 - Present)
Wayne County (1846 - Present)
Webster County (1853 - Present)
Winnebago County (1851 - Present)
Winneshiek County (1847 - Present)
Worth County (1851 - Present)
Wright County (1851 - Present)
Yell County (1853 - Present)