Wis. Stat. § 24.34

In the event that the sale of any public lands are made by mistake or not in accordance with law, or are obtained by fraud, or in the event that the state had no title to the lands sold, or the state's title has failed, the sale of the lands shall be void and no contract, certificate of purchase, or patent issued on the lands sold shall be of any effect, but the person named as vendee, or that person's successor in interest, may furnish to the board any proof that will satisfy the board of the facts. Except as provided in s. 24.341 , upon receipt of satisfactory proof of the facts asserted by the vendee, the board shall order all amounts, either of principal or interest, paid for the lands described in the contract, certificate, or patent, together with the interest on the amounts so paid from the time of each such payment, at the rate of 6 percent per year, simple interest, to be refunded and paid out of the state treasury, from the fund to which it has been credited, to the person entitled to the refund. Notwithstanding anything contained in this section, no money shall be paid to any person participating in any fraud in obtaining the land, as provided in this section.