Mo. Rev. Stat. § 71.920: City limits may be extended by ordinance if approved by unanimous affirmative vote in both elections — effective when.

In the event that the question of annexing such territory is approved by a unanimous affirmative vote in both the annexing municipality and the territory sought to be annexed, the annexing municipality, other provisions of this chapter notwithstanding, shall extend its limits by ordinance to include such territory, specifying with accuracy the new boundary lines to which the city, town, or village limits are extended, except that, no such ordinance by any municipality in a first class charter county which has a population of at least nine hundred thousand shall become effective sooner than one year after the date of the election approving the annexation. Upon duly enacting such annexation ordinance, the municipality shall cause three certified copies of the same to be filed with the clerk of the county wherein the municipality is located, whereupon the annexation shall be complete and final and thereafter all courts of this state shall take judicial notice of the limits of that municipality as so extended.