Iowa Code § 468.285: Levies — certificates and bonds.

After the amount to be assessed and levied against the several tracts of land shall have been finally determined, the several boards, acting separately, and within their own counties, shall levy and collect the taxes apportioned and levied in their respective counties. They may issue warrants, improvement certificates, or bonds for the payment of the cost of such improvement within their respective counties, with the same right of landowners to pay without interest or in installments all as provided where the district is wholly within one county.