Mo. Rev. Stat. § 108.040

Whenever it may become necessary for any county in this state to incur an indebtedness as authorized in section 108.010 or 108.020, it shall be lawful for any number of voters of such county, but not less than one percent or three hundred, whichever is greater, as determined by the vote for governor in the county in last election at which a governor was elected, to present to the county commission of such county a petition in writing setting forth the object and purpose for which the indebtedness is desired to be incurred and asking that the question be submitted to the voters. Upon the presentation of such petition it shall be the duty of the county commission of such county to order that the question be submitted to the voters.