Wis. Stat. § 198.07: Board of directors, boundaries.

(1) The government of each district shall be vested in a board of 5 directors.

(2) The boundaries of the subdistricts shall be drawn so that each shall contain approximately an equal number of voters, except that no municipality shall contain more than 2 subdistricts, nor shall any municipality be divided unless it shall comprise more than one subdistrict.

(3) Where a district includes a municipality that contains more than 50 percent of the voters in the entire district, all of the following apply:

(a) A director at large shall be appointed.

(b) The territory in the district, other than that contained in the municipality described in sub. (3) (intro.), shall be divided into 2 subdistricts.