Andrew (1841 from Platte Purchase), Benton (1835 from Pettis & St. Clair), Boone (1820 from Howard), Buchanan (1838 from Platte Purchase, Butler (1849 from Wayne), Carroll (1833 from Ray), Cass (1835 from Jackson), Cedar (1845 From Dade & St. Clair), Clark (1836 from Lewis), Clay (1822 from Ray), Cooper (1818 from Howard), Dade (1841 from Greene), Daviess (1836 from Ray), DeKalb (1845 from Clinton), Dunklin (1845 from Stoddard), Franklin (1818 from St. Louis), Gasconade (1820 from Franklin), Gentry (1841 from Clinton), Greene (1833 from Crawford), Grundy (1841 from Livingston), Hickory (1845 from Benton & Polk), Holt (1841 from Platte Purchase), Howard (1818 from St. Charles & St. Louis), Jackson (1826 from Lafayette), Jasper (1841 from Newton), Jefferson (1818 from Ste. Genevieve & St. Louis), Johnson (1834 from Lafayette), Lafayette (1820 from Cooper), Lincoln (1818 from St. Charles), Macon (1837 from Randolph), Madison (1818 from Cape Girardeau & Ste. Genevieve), Marion (1822 from Ralls), Mercer (1845 from Grundy), Monroe (1831 from Ralls), Montgomery (1818 from St. Charles), New Madrid (1812 Original District), Nodaway (1841 from Andrew), Ozark (1841 from Taney), Perry (1820 from St. Genevieve), Pike (1818 from St. Charles), Platte (1838 from Platte Purchase), Polk (1835 from Greene), Ralls (1820 from Pike), Randolph (1829 from Chariton), Ray (1820 from Howard, Saline (1820 from Cooper & Howard), Schuyler (1845 from Adair), Shelby (1835 from Marion), St. Charles (1812 Original District), St. Louis (1812 Original District. St. Louis is also an independent city predating the county, but is listed with the county for convenience.), Sullivan (1843 Linn), Washington (1813 from Ste. Genevieve), Wayne (1818 from Cape Giradeau
NOTE: County formation dates from "Handybook for Genealogists" by Everton Publishers.