Wis. Stat. § 236.33
It shall be unlawful to divide or subdivide and convey by deed or otherwise any lot in any recorded plat or any parcel or tract of unplatted land in any city of the first class so as to create a lot or parcel of land which does not have street or public highway frontage of at least 4 feet or an easement to a street or public highway of a minimum width of 4 feet but this section shall not apply to conveyances by tax deed or through the exercise of eminent domain or to such reductions in size or area as are caused by the taking of property for public purposes. This section shall not prohibit the dividing or subdividing of any lot or parcel of land in any such city where the divided or subdivided parts thereof which become joined in ownership with any other lot or parcel of land comply with the requirements of this section, if the remaining portion of such lot or parcel so divided or subdivided complies. Any person who shall make such conveyance or procure such a sale or act as agent in procuring such sale or conveyance shall be fined not less than $100 or more than $500 or imprisoned not more than 6 months or both.
Wis. Stat. § 236.33