Any time a voter moves from county to county or state to state, that voter will need to re-register to vote in their new county/state of residence.  If a voter is already registered and moves to a new residence located in the same county, that voter will need to update their registration, preferably before the day of the election.

The deadline to register to vote in any given election is 28 days prior to the election.  Voting in a county or precinct therein that does not represent your current residence on the day of the election is a violation of Missouri statute and is prosecutable by law.