Mo. Rev. Stat. § 137.385: Appeal from assessment — form — time for filing.

Any person aggrieved by the assessment of his property may appeal to the county board of equalization. An appeal shall be in writing and the forms to be used for this purpose shall be furnished by the county clerk. Such appeal shall be lodged with the county clerk as secretary of the board of equalization before the second Monday in July; provided, that the board may in its discretion extend the time for filing such appeals.