Nummeret i kolonnen med overskriften "#" er det nummer, der anvendes på kortet fra National Atlas of the United States, som er vist til venstre. Federal Information Processing Standard (FIPS)-koden, som USA's regering bruger til at identificere amter entydigt, er angivet ved hver post. FIPS-koden for hvert amt er forbundet med folketællingsdata for det pågældende amt.
| Amt | FIPS-kode | Amtssæde | # | Etableret | dannet af | Betydning af navnet | Befolkning | Område | Kort |
| Adair County | 001 | Greenfield | 69 | 15. januar, 1851 | Cass County | John Adair (1757-1840), sjette guvernør i Kentucky | 7003768200000000000♠7,682 | 70025690000000000000000♠569 km2 (70031474000000000000000♠1,474 km2) |  |
| Adams County | 003 | Corning | 81 | 15. januar, 1851 | Taylor County | John Adams, USA's anden præsident (1797-1801) | 7003402900000000000♠4,029 | 7002424240000000000000000♠424 km2 (700310980000000000000000000♠1,098 km2) |  |
| Allamakee County | 005 | Waukon | 11 | 20. februar, 1847 | Clayton County | Omstridt, muligvis opkaldt efter Allan Makee, en tidlig indianerhandler og guide for de første nybyggere | 7004143300000000000♠14,330 | 70026400000000000000000♠640 km2 (70031658000000000000000♠1,658 km2) |  |
| Appanoose County | 007 | Centerville | 96 | 17. februar, 1843 | Davis County | Appanoose, indianerhøvding, der ledede fredspartiet i Black Hawk-krigen | 7004128840000000000♠12,884 | 70024960000000000000000♠496 km2 (7003128500000000000♠1.285 km2) |  |
| Audubon County | 009 | Audubon | 57 | 15. januar, 1851 | Black Hawk County og Cass County | John James Audubon (1785-1851), ornitolog og kunstner | 7003611900000000000♠6,119 | 70024430000000000000000♠443 km2 (70031147000000000000000♠1,147 km2) |  |
| Benton County | 011 | Vinton | 51 | 21. december, 1837 | Amerikanske indianeres landområder og Wisconsin Territory | Thomas Hart Benton, amerikansk senator (1821-1851) | 7004260760000000000♠26,076 | 70027160000000000000000♠716 km2 (70031854000000000000000♠1,854 km2) |  |
| Black Hawk County | 013 | Waterloo | 39 | 17. februar, 1843 | Delaware County | Black Hawk (1767-1838), høvding for Fox and Sac-indianerne og leder af Black Hawk-krigen | 7005131090000000000♠131,090 | 70025670000000000000000♠567 km2 (700314690000000000000000000♠1,469 km2) |  |
| Boone County | 015 | Boone | 47 | 13. januar, 1846 | Polk County | Nathan Boone (1781-1863), en af de første til at kortlægge Iowa | 7004263060000000000♠26,306 | 70025720000000000000000♠572 km2 (70031481000000000000000♠1,481 km2) |  |
| Bremer County | 017 | Waverly | 30 | 15. januar, 1851 | Amerikanske indianeres landområder og Winnebago County | Fredrika Bremer (1801-1865), svensk digter og forfatter | 7004242760000000000♠24,276 | 7002428280000000000000000♠428 km2 (700311090000000000000000000♠1,109 km2) |  |
| Buchanan County | 019 | Uafhængighed | 40 | 21. december, 1837 | Delaware County og Wisconsin Territory | James Buchanan, USA's femtende præsident (1857-1861) | 7004209580000000000♠20,958 | 70025710000000000000000♠571 km2 (70031479000000000000000♠1,479 km2) |  |
| Buena Vista County | 021 | Storm Lake | 24 | 15. januar, 1851 | Clay County og Sac County | Slaget ved Buena Vista, et slag under den mexicansk-amerikanske krig | 7004202600000000000♠20,260 | 70025750000000000000000♠575 km2 (70031489000000000000000♠1,489 km2) |  |
| Butler County | 023 | Allison | 29 | 15. januar, 1851 | Black Hawk County og Buchanan County | William Orlando Butler (1791-1880), helt fra krigen i 1812 og forgæves kandidat til vicepræsidentposten | 7004148670000000000♠14,867 | 70025800000000000000000♠580 km2 (70031502000000000000000♠1,502 km2) |  |
| Calhoun County | 025 | Rockwell City | 34 | 15. januar, 1851 | Fox County (omdøbt) | John Caldwell Calhoun, USA's vicepræsident (1825-1832) | 7003967000000000000♠9,670 | 70025700000000000000000♠570 km2 (70031476000000000000000♠1,476 km2) |  |
| Carroll County | 027 | Carroll | 45 | 15. januar, 1851 | Guthrie County | Charles Carroll (1737-1832), den længstlevende underskriver af uafhængighedserklæringen | 7004208160000000000♠20,816 | 70025690000000000000000♠569 km2 (70031474000000000000000♠1,474 km2) |  |
| Cass County | 029 | Atlanterhavet | 68 | 15. januar, 1851 | Pottawattamie County | Lewis Cass, amerikansk senator fra Michigan og forgæves kandidat til præsidentvalget (1848) | 7004139560000000000♠13,956 | 70025640000000000000000♠564 km2 (70031461000000000000000♠1,461 km2) |  |
| Cedar County | 031 | Tipton | 65 | 21. december, 1837 | Wisconsin-territoriet | Red Cedar River, flod, der løber gennem amtet | 7004184990000000000♠18,499 | 70025800000000000000000♠580 km2 (70031502000000000000000♠1,502 km2) |  |
| Cerro Gordo County | 033 | Mason City | 17 | 15. januar, 1851 | Floyd County | Slaget ved Cerro Gordo, slag under den mexicansk-amerikanske krig | 7004441510000000000♠44,151 | 70025680000000000000000♠568 km2 (70031471000000000000000♠1,471 km2) |  |
| Cherokee County | 035 | Cherokee | 23 | 15. januar, 1851 | Crawford County | Den amerikanske indianerstamme Cherokee | 7004120720000000000♠12,072 | 70025770000000000000000♠577 km2 (70031494000000000000000♠1,494 km2) |  |
| Chickasaw County | 037 | Ny Hampton | 19 | 15. januar, 1851 | Fayette County | Den amerikanske indianerstamme Chickasaw | 7004124390000000000♠12,439 | 70025050000000000000000♠505 km2 (70031308000000000000000♠1,308 km2) |  |
| Clarke County | 039 | Osceola | 83 | 13. januar, 1846 | Lucas County | James Clarke, tredje guvernør i Iowa Territory (1845-1846) | 7003928600000000000♠9,286 | 70024310000000000000000♠431 km2 (70031116000000000000000♠1,116 km2) |  |
| Clay County | 041 | Spencer | 14 | 15. januar, 1851 | Amerikanske indianeres landområder | Henry Clay, Jr. (1807-1847), officer i den mexicansk-amerikanske krig | 7004166670000000000♠16,667 | 70025690000000000000000♠569 km2 (70031474000000000000000♠1,474 km2) |  |
| Clayton County | 043 | Elkader | 21 | 21. december, 1837 | Dubuque County og Wisconsin Territory | John M. Clayton (1796-1856), amerikansk senator fra Delaware | 7004181290000000000♠18,129 | 70027790000000000000000♠779 sq mi (700320180000000000000000000♠2,018 km2) |  |
| Clinton County | 045 | Clinton | 66 | 21. december, 1837 | Dubuque County og Wisconsin Territory | DeWitt Clinton (1769-1828), guvernør i New York | 7004491160000000000♠49,116 | 70026950000000000000000♠695 km2 (700318000000000000000000000♠1.800 km2) |  |
| Crawford County | 047 | Denison | 44 | 15. januar, 1851 | Shelby County | William Harris Crawford (1772-1834), amerikansk senator fra Georgia | 7004170960000000000♠17,096 | 70027140000000000000000♠714 km2 (700318490000000000000000000♠1,849 km2) |  |
| Dallas County | 049 | Adel | 59 | 13. januar, 1846 | Polk County | George Mifflin Dallas (1792-1864), USA's ellevte vicepræsident | 7004661350000000000♠66,135 | 70025860000000000000000♠586 km2 (700315180000000000000000000♠1,518 km2) |  |
| Davis County | 051 | Bloomfield | 97 | 17. februar, 1843 | Van Buren County | Garrett Davis (1801-1872), kongresmedlem | 7003875300000000000♠8,753 | 70025030000000000000000♠503 km2 (700313030000000000000000000♠1,303 km2) |  |
| Decatur County | 053 | Leon | 94 | 13. januar, 1846 | Appanoose County | Stephen Decatur (1779-1820), flådeofficer i krigen 1812 | 7003845700000000000♠8,457 | 70025320000000000000000♠532 km2 (700313780000000000000000000♠1,378 km2) |  |
| Delaware County | 055 | Manchester | 41 | 21. december, 1837 | Dubuque County og Wisconsin Territory | Delstaten Delaware, hjemsted for Iowas fortaler for statsdannelse Senator John M. Clayton fra USA | 7004177640000000000♠17,764 | 70025780000000000000000♠578 km2 (70031497000000000000000♠1,497 km2) |  |
| Des Moines County | 057 | Burlington | 89 | 6. september, 1834 | Michigan-territoriet og Wisconsin-territoriet | Des Moines River, flod, der engang løb gennem amtet | 7004403250000000000♠40,325 | 7002416000000000000000♠416 km2 (700310770000000000000000000♠1,077 km2) |  |
| Dickinson County | 059 | Spirit Lake | 3 | 15. januar, 1851 | Kossuth County | Daniel Stevens Dickinson (1800-1866), amerikansk senator fra New York | 7004166670000000000♠16,667 | 70023810010000000000000000♠381 km2 (700298700000000000000000000♠987 km2) |  |
| Dubuque County | 061 | Dubuque | 42 | 6. september, 1834 | Michigan-territoriet og Wisconsin-territoriet | Julien Dubuque (1762-1810), den første hvide bosætter i Iowa | 7004936530000000000♠93,653 | 70026080000000000000000♠608 km2 (700315750000000000000000000♠1,575 km2) |  |
| Emmet County | 063 | Estherville | 4 | 15. januar, 1851 | Dickinson County og Kossuth County | Robert Emmet (1778-1803), irsk revolutionær og amerikansk republikansk sympatisør | 7004103020000000000♠10,302 | 70023960000000000000000♠396 km2 (70031026000000000000000♠1,026 km2) |  |
| Fayette County | 065 | Vestunionen | 20 | 21. december, 1837 | Clayton County og Wisconsin Territory | Marquis de Lafayette (1757-1834), franskmand, der hjalp koloniale styrker under den amerikanske revolutionskrig | 7004208800000000000♠20,880 | 70027310000000000000000♠731 km2 (700318930000000000000000000♠1,893 km2) |  |
| Floyd County | 067 | Charles City | 18 | 15. januar, 1851 | Chickasaw County | Charles Floyd (1782-1804), medlem af Lewis og Clark-ekspeditionen, der døde i Iowa | 7004163030000000000♠16,303 | 70025010000000000000000♠501 km2 (700312980000000000000000000♠1,298 km2) |  |
| Franklin County | 069 | Hampton | 28 | 15. januar, 1851 | Chickasaw County | Benjamin Franklin (1706-1790), statsmand og USA's grundlægger | 7004106800000000000♠10,680 | 70025820000000000000000♠582 km2 (70031507000000000000000♠1,507 km2) |  |
| Fremont County | 071 | Sidney | 90 | 24. februar, 1847 | Pottawattamie County | John Charles Fremont (1813-1890), officer i den mexicansk-amerikanske krig | 7003744100000000000♠7,441 | 70025110000000000000000♠511 km2 (700313230000000000000000000♠1,323 km2) |  |
| Greene County | 073 | Jefferson | 46 | 15. januar, 1851 | Dallas County | Nathanael Greene (1742-1786), general fra den amerikanske revolutionskrig | 7003933600000000000♠9,336 | 70025680000000000000000♠568 km2 (70031471000000000000000♠1,471 km2) |  |
| Grundy County | 075 | Grundy Center | 38 | 15. januar, 1851 | Black Hawk County | Felix Grundy (1777-1840), amerikansk senator | 7004124530000000000♠12,453 | 70025030000000000000000♠503 km2 (700313030000000000000000000♠1,303 km2) |  |
| Guthrie County | 077 | Guthrie Center | 58 | 8. juli 1851 | Jackson County | Edwin B. Guthrie, officer i den mexicansk-amerikanske krig | 7004109540000000000♠10,954 | 70025910000000000000000♠591 km2 (70031531000000000000000♠1,531 km2) |  |
| Hamilton County | 079 | Webster City | 36 | 22. december 1856 | Webster County | William W. Hamilton, formand for senatet i Iowa (1856-1857) | 7004156730000000000♠15,673 | 70025770000000000000000♠577 km2 (70031494000000000000000♠1,494 km2) |  |
| Hancock County | 081 | Garner | 16 | 15. januar, 1851 | Wright County | John Hancock (1737-1793), formand for den første kontinentalkongres | 7004113410000000000♠11,341 | 70025710000000000000000♠571 km2 (70031479000000000000000♠1,479 km2) |  |
| Hardin County | 083 | Eldora | 37 | 15. januar, 1851 | Black Hawk County | John J. Hardin (1810-1847), fremtrædende soldat i Black Hawk-krigen | 17004175340000000000♠7,534 | 70025690000000000000000♠569 km2 (70031474000000000000000♠1,474 km2) |  |
| Harrison County | 085 | Logan | 55 | 15. januar, 1851 | Pottawattamie County | William Henry Harrison (1773-1841), USA's niende præsident | 7004149280000000000♠14,928 | 70026970000000000000000♠697 km2 (700318050000000000000000000♠1,805 km2) |  |
| Henry County | 087 | Mount Pleasant | 88 | 7. december, 1836 | Wisconsin-territoriet | Omstridt; enten Henry Dodge (1782-1867), guvernør i Wisconsin Territory; eller James Dougherty Henry, general i Black Hawk-krigen | 7004201450000000000♠20,145 | 70024340000000000000000♠434 km2 (700311240000000000000000000♠1,124 km2) |  |
| Howard County | 089 | Cresco | 9 | 15. januar, 1851 | Chickasaw County | Tilghman Ashurst Howard (1797-1844), kongresmedlem | 7003956600000000000♠9,566 | 70024730000000000000000♠473 km2 (700312250000000000000000000♠1,225 km2) |  |
| Humboldt County | 091 | Dakota City | 26 | 26. februar, 1857 | Webster County | Alexander von Humboldt (1769-1859), tysk videnskabsmand | 7003981500000000000♠9,815 | 70024340000000000000000♠434 km2 (700311240000000000000000000♠1,124 km2) |  |
| Ida County | 093 | Ida Grove | 32 | 15. januar, 1851 | Cherokee County | Mount Ida i Grækenland | 7003708900000000000♠7,089 | 70024320000000000000000♠432 km2 (700311190000000000000000000♠1,119 km2) |  |
| Iowa County | 095 | Marengo | 63 | 17. februar, 1843 | Washington County | Iowa River, flod, der løber gennem amtet, og som i sig selv er opkaldt efter den amerikanske indianerstamme Ioway | 7004163550000000000♠16,355 | 70025860000000000000000♠586 km2 (700315180000000000000000000♠1,518 km2) |  |
| Jackson County | 097 | Maquoketa | 54 | 21. december, 1837 | Wisconsin-territoriet | Andrew Jackson (1767-1845), USA's syvende præsident | 7004198480000000000♠19,848 | 70026360000000000000000♠636 km2 (70031647000000000000000♠1,647 km2) |  |
| Jasper County | 099 | Newton | 61 | 13. januar, 1846 | Mahaska County | William Jasper (1750-1779), sergent i den amerikanske revolutionskrig | 7004368420000000000♠36,842 | 70027300000000000000000♠730 km2 (70031891000000000000000♠1,891 km2) |  |
| Jefferson County | 101 | Fairfield | 87 | 21. januar, 1839 | Amerikanske indianeres landområder | Thomas Jefferson (1743-1826), USA's tredje præsident | 7004168430000000000♠16,843 | 70024350000000000000000♠435 km2 (70031127000000000000000♠1,127 km2) |  |
| Johnson County | 103 | Iowa City | 64 | 21. december, 1837 | Des Moines County, Iowa og Wisconsin Territory | Richard Mentor Johnson (1780-1850), USA's vicepræsident 1837-1841 | 7005130882000000000♠130,882 | 70026140000000000000000♠614 km2 (700315900000000000000000000♠1.590 km2) |  |
| Jones County | 105 | Anamosa | 53 | 21. december, 1837 | Wisconsin-territoriet | George Wallace Jones (1804-1896), amerikansk senator fra Iowa | 7004206380000000000♠20,638 | 70025750000000000000000♠575 km2 (70031489000000000000000♠1,489 km2) |  |
| Keokuk County | 107 | Sigourney | 74 | 21. december, 1837 | Washington County | Keokuk (1767-1848), høvding for den amerikanske indianerstamme Sac | 7004105110000000000♠10,511 | 70025790000000000000000♠579 km2 (70031500000000000000000♠1.500 km2) |  |
| Kossuth County | 109 | Algona | 5 | 15. januar, 1851 | Webster County | Lajos Kossuth (1802-1894), ungarsk revolutionær, der var inspireret af de amerikanske demokratiske idealer | 7004155430000000000♠15,543 | 70029730000000000000000♠973 km2 (70032520000000000000000♠2,520 km2) |  |
| Lee County | 111 | Fort Madison og Keokuk | 99 | 7. december, 1836 | Des Moines County | William Elliott Lee, forretningsmand fra New York Land Company, som solgte amtets første jordstykker | 7004358620000000000♠35,862 | 70025170000000000000000♠517 km2 (700313390000000000000000000♠1,339 km2) |  |
| Linn County | 113 | Cedar Rapids | 52 | 21. december, 1837 | Wisconsin-territoriet | Lewis Fields Linn (1795-1843), læge og amerikansk senator fra Missouri | 7005211226000000000♠211,226 | 70027180000000000000000♠718 km2 (700318600000000000000000000♠1,860 km2) |  |
| Louisa County | 115 | Wapello | 76 | 7. december, 1836 | Des Moines County | Omstridt; enten Louisa Massey, en kvinde, der dengang var berømt for at hævne sin brors død, eller Louisa County, Virginia | 7004113870000000000♠11,387 | 70024020000000000000000♠402 km2 (70031041000000000000000♠1,041 km2) |  |
| Lucas County | 117 | Chariton | 84 | 13. januar, 1846 | Monroe County | Robert Lucas (1781-1853), første guvernør i Iowa Territory | 7003889800000000000♠8,898 | 70024310000000000000000♠431 km2 (70031116000000000000000♠1,116 km2) |  |
| Lyon County | 119 | Rock Rapids | 1 | 15. januar, 1851 | Woodbury County, Iowa | Nathaniel Lyon (1818-1861), den første general fra Unionen, der blev dræbt i den amerikanske borgerkrig, (tidligere Buncombe County) | 7004115810000000000♠11,581 | 70025880000000000000000♠588 km2 (700315230000000000000000000♠1,523 km2) |  |
| Madison County | 121 | Winterset | 70 | 13. januar, 1846 | Polk County | James Madison (1751-1836), USA's fjerde præsident | 7004156790000000000♠15,679 | 70025610000000000000000♠561 km2 (70031453000000000000000♠1,453 km2) |  |
| Mahaska County | 123 | Oskaloosa | 73 | 17. februar, 1843 | Fox and Sac-indianernes landområder | Mahaska (1784-1834), høvding for Ioway-stammen af indianere | 7004223810000000000♠22,381 | 70025710000000000000000♠571 km2 (70031479000000000000000♠1,479 km2) |  |
| Marion County | 125 | Knoxville | 72 | 10. juni, 1845 | Washington County | Francis Marion (1732-1795), general i den amerikanske revolutionskrig | 7004333090000000000♠33,309 | 70025540000000000000000♠554 km2 (700314350000000000000000000♠1,435 km2) |  |
| Marshall County | 127 | Marshalltown | 49 | 13. januar, 1846 | Jasper County | John Marshall (1755-1835), fjerde øverste dommer ved USA's højesteret | 7004406480000000000♠40,648 | 70025720000000000000000♠572 km2 (7003148100000000000♠1,481 km2) |  |
| Mills County | 129 | Glenwood | 79 | 15. januar, 1851 | Pottawattamie County | Frederick Mills, major, dræbt under slaget ved Churubusco i den mexicansk-amerikanske krig | 7004150590000000000♠15,059 | 7002437000000000000♠437 km2 (700311320000000000000000000♠1,132 km2) |  |
| Mitchell County | 131 | Osage | 8 | 15. januar, 1851 | Chickasaw County | John Mitchel (1815-1875), irsk revolutionær, der i en periode opererede fra USA | 7004107760000000000♠10,776 | 70024690000000000000000♠469 km2 (700312150000000000000000000♠1,215 km2) |  |
| Monona County | 133 | Onawa | 43 | 15. januar, 1851 | Harrison County | Ord af indiansk oprindelse, der måske kan oversættes til "fredelig dal" | 7003924300000000000♠9,243 | 70026930000000000000000♠693 km2 (70031795000000000000000♠1,795 km2) |  |
| Monroe County | 135 | Albia | 85 | 17. februar, 1843 | Wapello County | James Monroe (1758-1831), USA's femte præsident | 7003797000000000000♠7,970 | 70024330000000000000000♠433 km2 (700311210000000000000000000♠1,121 km2) |  |
| Montgomery County | 137 | Rød eg | 80 | 15. januar, 1851 | Polk County | Richard Montgomery (1738-1775), general i den amerikanske revolutionskrig | 7004107400000000000♠10,740 | 7002424240000000000000000♠424 km2 (700310980000000000000000000♠1,098 km2) |  |
| Muscatine County | 139 | Muscatine | 77 | 7. december, 1836 | Des Moines County | Muscatine indianerstamme | 7004427450000000000♠42,745 | 70024390000000000000000♠439 km2 (70031137000000000000000♠1,137 km2) |  |
| O'Brien County | 141 | Primghar | 13 | 15. januar, 1851 | Cherokee County | William Smith O'Brien (1803-1864), irsk revolutionær, der var inspireret af de amerikanske demokratiske idealer | 7004143980000000000♠14,398 | 70025730000000000000000♠573 km2 (70031484000000000000000♠1,484 km2) |  |
| Osceola County | 143 | Sibley | 2 | 15. januar, 1851 | Woodbury County | Osceola (1804-1838), indiansk leder | 7003646200000000000♠6,462 | 70023990000000000000000♠399 km2 (700310330000000000000000000♠1,033 km2) |  |
| Side County | 145 | Clarinda | 91 | 24. februar, 1847 | Pottawattamie County | John Page, officer dræbt i slaget ved Palo Alto i den mexicansk-amerikanske krig | 7004159320000000000♠15,932 | 7002535350000000000000000♠535 km2 (700313860000000000000000000♠1,386 km2) |  |
| Palo Alto County | 147 | Emmetsburg | 15 | 15. januar, 1851 | Kossuth County | Slaget ved Palo Alto i den mexicansk-amerikanske krig | 7003942100000000000♠9,421 | 70025640000000000000000♠564 km2 (70031461000000000000000♠1,461 km2) |  |
| Plymouth County | 149 | Le Mars | 22 | 15. januar, 1851 | Woodbury County | Landingssted for de pilgrimme, der kom til Amerika med Mayflower | 7004249860000000000♠24,986 | 70028640000000000000000♠864 km2 (700322380000000000000000000♠2,238 km2) |  |
| Pocahontas County | 151 | Pocahontas | 25 | 15. januar, 1851 | Greene County og Humboldt County | Pocahantas (1595-1618), berømt indiansk kvinde | 7003731000000000000♠7,310 | 70025780000000000000000♠578 km2 (70031497000000000000000♠1,497 km2) |  |
| Polk County | 153 | Des Moines | 60 | 13. januar, 1846 | Amerikanske indianeres landområder | James K. Polk (1795-1849), USA's ellevte præsident | 7005430640000000000♠430,640 | 70025700000000000000000♠570 km2 (70031476000000000000000♠1,476 km2) |  |
| Pottawattamie County | 155 | Council Bluffs | 67 | 24. februar, 1847 | Amerikanske indianeres landområder | Pottawattamie indianerstamme | 7004931580000000000♠93,158 | 70029540000000000000000♠954 km2 (70032471000000000000000♠2,471 km2) |  |
| Poweshiek County | 157 | Montezuma | 62 | 17. februar, 1843 | Mesquakie indianske områder | Poweshiek, høvding for ræve-stammen | 7004189140000000000♠18,914 | 70025850000000000000000♠585 km2 (700315150000000000000000000♠1,515 km2) |  |
| Ringgold County | 159 | Mount Ayr | 93 | 24. februar, 1847 | Taylor County | Samuel Ringgold (1796-1846), major, dræbt i den mexicansk-amerikanske krig | 7003513100000000000♠5,131 | 70025380000000000000000♠538 km2 (700313930000000000000000000♠1,393 km2) |  |
| Sac County | 161 | Sac City | 33 | 15. januar, 1851 | Greene County | Sac indianerstamme | 7004103500000000000♠10,350 | 70025760000000000000000♠576 km2 (70031492002000000000000000♠1,492 km2) |  |
| Scott County | 163 | Davenport | 78 | 21. december, 1837 | Wisconsin-territoriet | Winfield Scott (1786-1866), general i den amerikanske hær under krigen i 1812 | 7005165224000000000♠165,224 | 70024580000000000000000♠458 km2 (70031186000000000000000♠1,186 km2) |  |
| Shelby County | 165 | Harlan | 56 | 15. januar, 1851 | Cass County | Isaac Shelby (1750-1826), general i den amerikanske revolutionskrig og krigen i 1812 | 7004121670000000000♠12,167 | 70025910000000000000000♠591 km2 (70031531000000000000000♠1,531 km2) |  |
| Sioux County | 167 | Orange City | 12 | 15. januar, 1851 | Plymouth County | Sioux indianerstamme | 7004337040000000000♠33,704 | 70027680000000000000000♠768 km2 (70031989000000000000000♠1,989 km2) |  |
| Story County | 169 | Nevada | 48 | 13. januar, 1846 | Boone County, Jasper County og Polk County | Joseph Story (1779-1845), dommer ved USA's højesteret | 7004895420000000000♠89,542 | 70025730000000000000000♠573 km2 (70031484000000000000000♠1,484 km2) |  |
| Tama County | 171 | Toledo | 50 | 17. februar, 1843 | Benton County og Boone County | Omstridt; enten Taimah, rævehøvding, eller Taomah, Poweshiek's hustru | 7004177670000000000♠17,767 | 70027210000000000000000♠721 km2 (700318670000000000000000000♠1,867 km2) |  |
| Taylor County | 173 | Bedford | 92 | 24. februar, 1847 | Side County | Zachary Taylor (1784-1850), USA's tolvte præsident | 7003631700000000000♠6,317 | 70025340000000000000000♠534 km2 (700313830000000000000000000♠1,383 km2) |  |
| Union County | 175 | Creston | 82 | 15. januar, 1851 | Clarke County | Staternes union | 7004125340000000000♠12,534 | 7002424240000000000000000♠424 km2 (700310980000000000000000000♠1,098 km2) |  |
| Van Buren County | 177 | Keosauqua | 98 | 7. december, 1836 | Des Moines County | Martin Van Buren (1782-1862), USA's ottende præsident | 7003757000000000000♠7,570 | 70024850000000000000000♠485 km2 (70031256000000000000000♠1,256 km2) |  |
| Wapello County | 179 | Ottumwa | 86 | 17. februar, 1843 | Amerikanske indianeres landområder | Wapello, høvding for den amerikanske stamme Fox Native American | 7004356250000000000♠35,625 | 70024320000000000000000♠432 km2 (700311190000000000000000000♠1,119 km2) |  |
| Warren County | 181 | Indianola | 71 | 13. januar, 1846 | Polk County | Joseph Warren (1741-1775), general i den amerikanske revolutionskrig | 7004462250000000000♠46,225 | 70025720000000000000000♠572 km2 (70031481000000000000000♠1,481 km2) |  |
| Washington County | 183 | Washington | 75 | 25. januar, 1839 | Wisconsin-territoriet | George Washington (1732-1799), USA's første præsident | 7004217040000000000♠21,704 | 70025690000000000000000♠569 km2 (70031474000000000000000♠1,474 km2) |  |
| Wayne County | 185 | Corydon | 95 | 13. januar, 1846 | Appanoose County | Anthony Wayne (1745-1796), general i den amerikanske revolutionskrig | 7003640300000000000♠6,403 | 7002526260000000000000000♠526 km2 (70031362000000000000000♠1,362 km2) |  |
| Webster County | 187 | Fort Dodge | 35 | 12. januar, 1853 | Risley County og Yell County (nedlagte amter) | Daniel Webster (1782-1852), amerikansk senator fra Massachusetts | 7004380130000000000♠38,013 | 70027150000000000000000♠715 km2 (70031852000000000000000♠1,852 km2) |  |
| Winnebago County | 189 | Forest City | 6 | 15. januar, 1851 | Kossuth County | Den amerikanske indianerstamme Winnebago | 7004108660000000000♠10,866 | 700240000000000000000000000♠400 km2 (700310360000000000000000000♠1,036 km2) |  |
| Winneshiek County | 191 | Decorah | 10 | 20. februar, 1847 | Amerikanske indianeres landområder | Winneshiek, høvding for den amerikanske indianerstamme Winnebago | 7004210560000000000♠21,056 | 70026900000000000000000♠690 km2 (70031787000000000000000♠1,787 km2) |  |
| Woodbury County | 193 | Sioux City | 31 | 12. januar, 1853 | Polk County | Levi Woodbury (1789-1851), guvernør i New Hampshire, (tidligere kaldet Wahkaw County) | 7005102172000000000♠102,172 | 70028730000000000000000♠873 km2 (70032261000000000000000♠2,261 km2) |  |
| Worth County | 195 | Northwood | 7 | 15. januar, 1851 | Mitchell County | William Jenkins Worth (1794-1849), officer i Black Hawk-krigen og den mexicansk-amerikanske krig | 7003759800000000000♠7,598 | 700240000000000000000000000♠400 km2 (700310360000000000000000000♠1,036 km2) |  |
| Wright County | 197 | Clarion | 27 | 15. januar, 1851 | Webster County og Kossuth County | Silas Wright (1795-1847), guvernør i New York, og Joseph Albert Wright (1810-1867), guvernør i Indiana, brødre | 7004132290000000000♠13,229 | 70025810000000000000000♠581 km2 (70031505000000000000000♠1,505 km2) |  |