Mo. Rev. Stat. § 108.010

Any county in this state, by vote of the constitutionally required percentage of the voters voting thereon, may become indebted in an amount exceeding in any year the income and revenue provided for such year plus any unencumbered balances from previous years. Such indebtedness shall not exceed five percent of the value of taxable tangible property therein as shown by the last completed assessment for state and county purposes.