.....though there is an exception if you are an IL resident since IA and IL are reciprocal tax states.
An IL resident working in IA would notify the IA employer of that (some form to fill out)...then the IA employer would withhold only IL taxes (or neither IL nor IA taxes if they are not registered to pay IL withholding)...then you would not indicate you had Other State Income since all of it is treated as-if earned in IL.