Wis. Stat. § 83.06: Maintenance of county aid highways.

All streets and highways improved with county aid under this chapter shall be maintained by the towns, cities and villages in which they lie but this provision shall not diminish or otherwise affect the duty of the county with respect to any street or highway which is a portion of the county trunk highway system, nor the powers of the county conferred by s. 83.03 (1) and (2) or s. 83.035.