Wis. Stat. § 231.25: Tax exemption.

The exercise of the powers granted by this chapter will be in all respects for the benefit of the people of this state, for the increase of their commerce, welfare and prosperity, and for the improvement of their health and living conditions, and as the operation and maintenance of a project undertaken pursuant to this chapter will constitute the performance of an essential public function, neither the authority nor any agent with which it contracts to operate or maintain a project is required to pay any taxes or assessments, including mortgage recording taxes, upon or in respect of a project or any property acquired or used by the authority or its agent under this chapter and the authority’s income therefrom shall at all times be free from taxation of every kind by the state and by political subdivisions of the state.