Iowa Code § 357D.3: Limitation on area.

A district may include all or parts of the unincorporated areas of one township and any unincorporated areas of adjoining townships or parts of adjoining townships, but shall not include property assessed as agricultural land, centrally assessed property, or manufacturing personal and real property. Except for property assessed as agricultural land, the owners of centrally assessed property or manufacturing property shall have the option to be included in the district.