Okay, speaking from personal experience here:
Missouri and Arkansas–especially those counties that are in the Ozarks region tend to have little or no building codes for personal residences –unless you plan to rent or sell them–Northeast section of Vermont is similar.Also, remote sections of Oklahoma, Kansas, Wyoming, Montana, Idaho, Oregon and Washington.
The main problem in all areas of the US is water. If there are wetlands on the property or a creek, there is always the issue of sewage disposal. Finding locales that are friendly to composting toilets and greywater systems can be a hassle.
I’ll forage around a bit in state gov. sites and see what I come up with for you!