Mo. Rev. Stat. § 578.105

If any county of the first class having a charter form of government containing the major portion of a city of over four hundred fifty thousand inhabitants exempts itself from the application of section 578.100 by a vote of the voters of the county pursuant to provisions of law permitting such vote, then a county in the following classification may also exempt itself from the application of section 578.100: Any county of the second class as of 1977 that is adjacent to any county containing a portion of a city with a population of more than four hundred thousand inhabitants in the 1970 census. The county may exempt itself from the provisions of section 578.100 by submission of the proposition to the voters of the county at a general election or a primary election, and the proposition receiving a majority of the votes cast therein. The proposal to exempt the county from the provisions of section 578.100 shall be submitted to the voters of the county upon a majority vote of the governing body of the county or when a petition requesting the submission of the proposal to the voters and signed by a number of qualified voters residing in the county equal to eight percent of the votes cast in the county in the next preceding gubernatorial election is filed with the governing body of the county. The ballot of submission shall contain, but not be limited to, the following language: