Sounds like CA and IA work differently. 45 is the speed limit for that highway because it's windy. On the straighter roads, the limit is usually 50-55. However, there are still no speed zones (as you call them) for small clusters of houses.
The only time I see otherwise is if mountains or rivers are involved, or there is density (in which case it is sure to be zoned!).
With very low traffic density, you might build the house closer to the road (maybe 10m off, separated with trees) for just that reason – to save land. (Not all rural houses are farms.)