Iowa Code § 468.141
The board of supervisors of any county shall have jurisdiction to establish subdrainage districts of lands included within a district extending into two or more counties when the lands to compose such subdistricts lie wholly within such county, and to make improvements therein, repair and maintain the same, fix and levy assessments for the payment thereof, and the provisions of this section shall apply to all such drainage subdistricts, the lands of which lie wholly within one county. The proceedings for all such purposes shall be the same as for the establishment, construction, and maintenance of an original levee or drainage district the lands of which lie wholly within one county, so far as applicable, except that one or more persons may petition for a subdistrict as provided in section 468.63.
Iowa Code § 468.141