Mo. Rev. Stat. § 137.375
1. The assessor shall make out and return to the county commission, on or before the first day of July in every year, the assessor's book, verified by his affidavit annexed thereto, in the following words:
______ being duly sworn makes oath and says that he has made diligent efforts to ascertain all the taxable property being or situate on the first day of January last past, in the county of which he is assessor; that, so far as he has been able to ascertain the same, it is correctly set forth in the foregoing book, in the manner and the value thereof stated therein, according to the mode required by law.
(L. 1945 p. 1930 § 10, A.L. 1959 H.B. 108, A.L. 2008 S.B. 711)