Mo. Rev. Stat. § 488.035: Witness in criminal proceedings, mileage allowance and per diem.

If the witness is summoned to attend and testify in this state, pursuant to the provisions of section 491.420, he or she shall, pursuant to section 491.420, be tendered by the treasurer of the county in which the prosecution is pending the sum of ten cents a mile for each mile by the ordinary traveled route to and from the court where the prosecution is pending and fifteen dollars for each day that he or she is required to travel and attend as a witness.