Iowa Code § 468.517
The canvass of the returns by the board or boards of supervisors shall be on the next Monday following the election. If the district is in more than one county, the board of supervisors of the county with the greatest acreage in the district shall canvass the vote. The board of supervisors of the other counties in which the district is located may attend and participate in the canvass of the returns. The board or boards of supervisors shall make a return of the results of the canvass to the auditor, who shall issue certificates to the trustees elected. When the district extends into more than one county, then the auditor with whom the election returns were filed shall issue the certificates and certify an abstract of the canvass to each other county in which the district is located.
Iowa Code § 468.517