Wis. Stat. § 704.22: Service of process in residential tenancy on nonresident party.

(1) A party to a residential tenancy in this state who is not a resident of this state shall designate an agent to accept service of process in this state for an action involving the tenancy. The agent shall be a resident of this state or a corporation authorized to do business in this state. If a party is a corporation, the agent is the corporation’s registered agent.

(2) Designation of an agent under sub. (1) shall be in writing and filed with the department of financial institutions.