On July 6, the Iowa Secretary of State posted the July 1 registration data. The percentages: Republican 33.03%; Democratic 30.73%; Libertarian .47%; Green .15%; independent and miscellaneous 35.62%.

In November 2016 the percentages had been: Republican 33.17%; Democratic 31.51%; Libertarian .42%; Green .13%; independent and miscellaneous 34.76%.