Iowa Code § 43.90
The county convention shall be composed of delegates elected at the last preceding precinct caucus. Delegates shall be persons who are or will by the date of the next general election become eligible electors and who are residents of the precinct. The number of delegates from each voting precinct shall be determined by a ratio adopted by the respective party county central committees, and a statement designating the number from each voting precinct in the county shall be filed by such committee not later than the time the list of precinct caucus meeting places required by section 43.4 is filed in the office of the commissioner. If the required statement is not filed, the commissioner shall fix the number of delegates from each voting precinct.
Iowa Code § 43.90