Wis. Stat. § 6.21: Deceased electors.

When by due proof it appears to the inspectors or, in municipalities where absentee ballots are canvassed under s. 7.52, when by due proof it appears to the board of absentee ballot canvassers that a person casting an absentee ballot at an election has died before the date of the election, the inspectors or board of absentee ballot canvassers shall return the ballot with defective ballots to the issuing official. The casting of the ballot of a deceased elector does not invalidate the election.