Wis. Stat. § 75.27
No action shall be maintained by the former owner or any person claiming under the former owner to recover the possession of any land or any interest therein which shall have been conveyed by deed for the nonpayment of taxes or to avoid such deed against any person claiming under such deed unless such action shall be brought within 3 years next after the recording of such deed. Whenever any such action shall be commenced upon any tax deed heretofore or hereafter issued after the expiration of 3 years from the date of the recording of such deed, such deed, if executed substantially in the form prescribed by law for the execution of tax deeds, shall be conclusive evidence of the existence and legality of all proceedings from and including the assessment of the property for taxation up to and including the execution of such deed.
Wis. Stat. § 75.27