Mo. Rev. Stat. § 52.140
In all such counties where the collector of the revenue is required by section 52.120 to maintain a branch office as provided in section 52.120, he shall be allowed to retain, in addition to the amount now authorized by law, three-fourths of one percent of all taxes collected to cover the additional expense of maintaining such branch office. If the amount retained under this section is more than sufficient to pay the salaries for the deputy and clerical hire in the branch office and for the mileage of the collector in traveling to and from such branch office at the rate allowed as the established per-mile allowance as a deduction by the Internal Revenue Service and other necessary travel expenses, all excess amounts shall be paid into the county treasury.
§ 52.140, RSMo
Effective 3/6/1979