There can never be more voters who cast a ballot in a jurisdiction than there are voters who are registered to vote in that jurisdiction, once a final number of registered voters for that jurisdiction has been calculated.
Calculating turnout after Election Day can suffer from numerous pitfalls, including the fact that the statistics from the election are not final until the election has been certified; people calculate turnout in different ways; and people can make mistakes in calculating turnout.
One way to calculate turnout is by dividing the total number of voters who cast a ballot in a reporting unit (the numerator) by the total number of registered voters in that reporting unit (the denominator).
Using this method in Wisconsin is complicated by the fact that voters are allowed to register on Election Day. If you do not include the number of voters who registered on Election Day in the denominator, it’s possible you will calculate a turnout figure that is greater than 100% for that reporting unit. This does not mean there were more voters who cast a ballot than voters who live in the jurisdiction. This simply means that the turnout calculation likely does not include the number of Election Day registrants in the denominator.
In many jurisdictions, clerks do not immediately publish the number of Election Day registrants, as they have 45 days to enter that data into the statewide system.
Calculating turnout using this method is further complicated by the fact that arriving at the number of active, registered voters on Election Day requires the person calculating the turnout to account for any registered voters in that jurisdiction that moved away before Election Day. An accurate estimate of this number would not be known until all Wisconsin clerks have entered their election information into the statewide database. Finally, large influxes of registered voters in certain wards or reporting units is a common occurrence, typically arising when a new apartment building or other multi-unit housing is built.