Wis. Stat. § 303.03: Prison labor on farms and buildings.

The wardens and the superintendents of the state prisons may employ inmates outside the institution’s yard in cultivating the farms or in doing any necessary work in the prosecution of the regular business of the institution or of other state institutions or of any other activity of the state or of any political subdivision thereof or in the construction of buildings by the state; and any such inmate who escapes shall be deemed as having escaped from the institution proper.