| County | Established | Seat | Territory From |
|---|---|---|---|
| Adair | 1/29/1841 | Kirksville | Macon, , , |
| Andrew | 1/29/1841 | Savannah | Platte Purchase, , , |
| Atchison | 2/14/1845 | Rockport | Holt, , , |
| Audrain | 12/17/1836 | Mexico | Callaway, Monroe, Ralls, |
| Barry | 1/5/1835 | Cassville | Greene, , , |
| Barton | 12/12/1855 | Lamar | Jasper, , , |
| Bates | 1/29/1841 | Butler | Van Buren, , , |
| Benton | 1/3/1835 | Warsaw | Greene, Pettis, , |
| Bollinger | 3/1/1851 | Marble Hill | Cape Girardeau, Madison, Stoddard, Wane |
| Boone | 1/1/1821 | Columbia | Howard, , , |
| Buchanan | 12/31/1838 | Saint Joseph | Platte Purchase, , , |
| Butler | 2/27/1849 | Poplar Bluff | Wayne, , , |
| Caldwell | 12/29/1836 | Kingston | Ray, , , |
| Callaway | 11/25/1820 | Fulton | Howard, Boone, Montgomery, |
| Camden | 1/29/1841 | Camdenton | Pulaski, Morgan, Benton, |
| Cape Girardeau | 10/1/1812 | Jackson | , , , |
| Carroll | 1/2/1833 | Carrollton | Ray, , , |
| Carter | 3/10/1859 | Van Buren | Ripley, Reynolds, Shannon, Oregon |
| Cass | 3/3/1835 | Harrisonville | Jackson, , , |
| Cedar | 2/14/1845 | Stockton | Dade, Saint Clair, , |
| Chariton | 1/1/1821 | Keytesville | Howard, , , |
| Christian | 3/8/1859 | Ozark | Greene, Taney, Webster, |
| Clark | 12/16/1836 | Kahoka | Lewis, , , |
| Clay | 1/2/1822 | Liberty | Ray, , , |
| Clinton | 1/2/1833 | Plattsburg | Clay, , , |
| Cole | 1/1/1821 | Jefferson City | Cooper, , , |
| Cooper | 2/1/1819 | Boonville | Howard, , , |
| Crawford | 1/23/1829 | Steelville | Gasconade, , , |
| Dade | 1/29/1841 | Greenfield | Polk, Barry, , |
| Dallas | 1/29/1841 | Buffalo | Polk, , , |
| Daviess | 12/29/1836 | Gallatin | Ray, , , |
| De Kalb | 2/25/1845 | Maysville | Clinton, , , |
| De Witt | Name given to area later Pulaski County | , , , | |
| Dent | 2/10/1851 | Salem | Shannon, Crawford, , |
| Dewitt | , , , | ||
| Dodge | Now in Iowa, included Putnam County area | , , , | |
| Douglas | 10/29/1857 | Ava | Ozark, , , |
| Dunklin | 2/14/1845 | Kennett | Stoddard, , , |
| Franklin | 1/1/1819 | Union | Saint Louis, , , |
| Gasconade | 1/1/1821 | Hermann | Franklin, , , |
| Gentry | 2/14/1845 | Albany | Clinton, , , |
| Greene | 1/2/1833 | Springfield | Crawfod, Wayne, , |
| Grundy | 1/29/1841 | Trenton | Livingston, , , |
| Harrison | 2/14/1845 | Bethany | Daviess, , , |
| Henry | 12/13/1834 | Clinton | Lafayette, , , |
| Hickory | 2/14/1845 | Hermitage | Benton, Polk, , |
| Holt | 1/29/1841 | Oregon | Platte Purchase, , , |
| Howard | 3/1/1816 | Fayette | Saint Louis, Saint Charles, , |
| Howell | 3/2/1857 | West Plains | Oregon, , , |
| Indian | , , , | ||
| Iron | 2/17/1857 | Ironton | Madion, Saint Francois, Washington, Reynolds |
| Jackson | 12/15/1826 | Independence | Lafayette, , , |
| Jasper | 1/29/1841 | Carthage | Barry, , , |
| Jefferson | 1/1/1819 | Hillsboro | Saint Louis, Ste. Genevieve, , |
| Johnson | 12/13/1834 | Warrensburg | Lafayette, , , |
| Knox | 2/14/1845 | Edina | Scotland, , , |
| Laclede | 2/24/1849 | Lebanon | Pulaski, Wright, Camden, |
| Lafayette | 1/1/1821 | Lexington | Cooper, , , |
| Lawrence | 2/14/1845 | Mount Vernon | Barry, Dade, , |
| Lewis | 1/2/1833 | Monticello | Marion, , , |
| Lincoln | 1/1/1819 | Troy | Saint Charles, , , |
| Linn | 1/6/1837 | Linneus | Chariton, , , |
| Livingston | 1/6/1837 | Chillicothe | Carroll, , , |
| Macon | 1/6/1837 | Macon | Chariton, Randolph, , |
| Madison | 1/1/1819 | Fredericktown | Cape Girardeau, Ste. Genevieve, , |
| Maries | 3/2/1855 | Vienna | Pulaski, Osage, , |
| Marion | 12/23/1826 | Palmyra | Ralls, , , |
| Mc Donald | 3/3/1849 | Pineville | Newton, , , |
| Mercer | 2/14/1845 | Princeton | Grundy, , , |
| Miller | 2/6/1837 | Tuscumbia | Pulaski, Cole, , |
| Mississippi | 2/14/1845 | Charleston | Scott, , , |
| Moniteau | 2/14/1845 | California | Morgan, Cole, , |
| Monroe | 1/6/1831 | Paris | Ralls, , , |
| Montgomery | 1/1/1819 | Montgomery City | Saint Charles, , , |
| Morgan | 1/5/1833 | Versailles | Cooper, , , |
| New Madrid | 10/1/1812 | New Madrid | , , , |
| Newton | 12/31/1838 | Neosho | Barry, , , |
| Niangua | Name chg’d to Dallas | , , , | |
| Nodaway | 2/14/1845 | Maryville | Andrew, , , |
| Oregon | 2/14/1845 | Alton | Ripley, , , |
| Osage | 1/29/1841 | Linn | Gasconade, , , |
| Ozark | 1/29/1841 | Gainesville | Taney, , , |
| Pemiscot | 2/19/1851 | Caruthersville | New Madrid, , , |
| Perry | 1/1/1821 | Perryville | Ste. Genevieve, , , |
| Pettis | 1/26/1833 | Sedalia | Cooper, Saline, , |
| Phelps | 11/13/1857 | Rolla | Crawfod, , , |
| Pike | 2/1/1819 | Bowling Green | Saint Charles, , , |
| Platte | 12/31/1838 | Platte City | Platte Purchase, , , |
| Polk | 1/5/1835 | Bolivar | Greene, , , |
| Pulaski | 1/19/1833 | Waynesville | Crawfod, , , |
| Putnam | 2/28/1845 | Unionville | Adair, Sullivan, , |
| Ralls | 1/1/1821 | New London | Pike, , , |
| Randolph | 1/23/1829 | Huntsville | Chariton, Ralls, , |
| Ray | 1/1/1821 | Richmond | Howard, , , |
| Reynolds | 2/25/1845 | Centerville | Shannon, , , |
| Ripley | 1/5/1833 | Doniphan | Wayne, , , |
| Rives | Name chg'd to Henry | , , , | |
| Saint Charles | 10/1/1812 | Saint Charles | , , , |
| Saint Clair | 1/29/1841 | Osceola | Rives, , , |
| Saint Francois | 12/19/1821 | Farmington | Ste. Genevieve, Washington, Jefferson, |
| Saint Louis | 10/1/1812 | Clayton | , , , |
| Saint Louis (City) | 10/1/1876 | Saint Louis | Saint Louis, , , |
| Saline | 1/1/1821 | Marshall | Cooper, , , |
| Schuyler | 2/14/1845 | Lancaster | Adair, , , |
| Scotland | 1/29/1841 | Memphis | Clark, Lewis, Shelby, |
| Scott | 3/1/1822 | Benton | New Madrid, , , |
| Seneca | , , , | ||
| Shannon | 1/29/1841 | Eminence | Ripley, , , |
| Shelby | 1/2/1835 | Shelbyville | Marion, , , |
| Ste. Genevieve | 10/1/1812 | Ste. Genevieve | , , , |
| Stoddard | 1/2/1835 | Bloomfield | New Madrid, , , |
| Stone | 2/10/1851 | Galena | Taney, , , |
| Sullivan | 2/14/1845 | Milan | Linn, , , |
| Taney | 1/6/1837 | Forsyth | Greene, , , |
| Texas | 2/14/1845 | Houston | Shannon, Wright, , |
| Unlisted | , , , | ||
| Van Buren | Name chg'd to Cass | , , , | |
| Vernon | 2/27/1855 | Nevada | Bates, , , |
| Warren | 1/5/1833 | Warrenton | Montgomery, , , |
| Washington | 11/1/1813 | Potosi | Ste. Genevieve, , , |
| Wayne | 2/1/1819 | Greenville | Cape Girardeau, , , |
| Webster | 3/3/1855 | Marshfield | Greene, , , |
| Worth | 2/25/1861 | Grant City | Gentry, , , |
| Wright | 1/29/1841 | Hartville | Pulaski, , , |
Updated: 12/29/2013 14:18:24