Iowa Code § 9F.2: Federal census.

The secretary of state shall, whenever a general census is taken by the federal government, procure from the supervisor of such census, or other proper federal official, a copy of such part of said census as gives the population of the state of Iowa by counties, by townships, and by cities, and file the same in the secretary of state’s office and attach thereto, dated and signed by the secretary, a certificate that the same is the census report furnished by said federal official.