From http://www.sos.mo.gov/archives/resources/census.asp
there is also a link to Local Historical, Museum, and Genealogical Agencies:Missouri Census Records
The need for statistical information about the population by the government of Missouri Territory resulted in the taking of a state census in the years 1814 and 1817. These census records listed only free white males. The next census was taken in 1821, the year statehood was achieved. Beginning in 1824 and following at four year intervals through 1876, other state censuses were taken.
The Census Act of 1824 and thereafter required that the sheriffs or assessors submit abstracts of their returns to the Secretary of State and that they file the original returns with the Clerks of the County Courts. Only a very few of the state census enumerations have survived. Below is a list of the surviving censuses.
Census Year County(ies)
1840 New Madrid, Newton, Pike, Randolph, Ray, Rives(later Henry), Shelby, Stoddard, and Warren
1844 Callaway, Greene
1856 Audrain
1868 Cape Girardeau
1876 Atchison, Benton, Butler, Callaway, Cape Girardeau, Christian, Daviess, Franklin, Gasconade, Greene, Holt, Howard, McDonald, Madison, Moniteau, Montogomery, Osage, Perry, Phelps, Reynolds, Ripley, St. Francois, Stone, Texas, Webster, and Worth
http://www.sos.mo.gov/archives/resources/links.asp