Wis. Stat. § 75.40

Such action must 1275.40 TAX SALES be brought in the circuit court of the county in which the lands or some parcel of them, the title of which is sought to be barred by such action, are situated. The county, as plaintiff in such action, may include in its complaint all the lands described in such conveyance, or any separate parcel, or as many separate parcels thereof as it sees fit. The county shall make defendants of all persons who were the former owners of the several parcels of land included in the complaint or those claiming under them or claiming any interest therein.