Wis. Stat. § 32.70: Statute of limitations.

Unless the action commences within one year after January 1 following the date the assessment of benefits is placed on the tax roll under s. 32.58 (2), no person may contest the sale of property or issuance of any tax certificate for nonpayment of an assessment. Commencing an action is subject to s. 32.61 and does not prevent the issuance or payment of any bonds issued under s. 32.67 or 32.69.