Mo. Rev. Stat. § 137.510: Assessor's books — method of preparation — date to be completed.

The assessor shall make up the assessment plat books or records in convenient alphabetical or numerical order from the reports made by the deputy assessors, the lists, statements or returns made of real or tangible personal property, his own view, or the best information he can otherwise obtain, and complete said assessment plat books or records on or before July first of each year.