As far as im aware, a good part of rural US does not have codes. But you usually have to be a good ways out of any big cities. Im currently building super efficient house in rural missouri, Im not extremely far out of town but i have no building codes here, however we do have septic codes, but i can take the test and still do the work myself(although it would have been much cheaper and easier to not have to deal with it). Most of the state doesnt have any codes, just near the cities. I suspect much of the US is like this.
If your just going to up and move anywhere, i would reevaluate the search to first prioritize the following: local resources, planting/grazing land, climate, rainfall, scenery, location to other things, local community, do you like the area, can you find work there, etc.
Then find some areas that have what your looking for and start searching on the internet. The codes, or lack of, vary county by county within the state. So you will search for that county on the net to see if they have building or septic codes, it might require calling some county department to find out but you will figure it out. If they have codes, just look up the next county over and so on until you find what your looking for.
Searching online is great, but it cant show you everything. If you find something you think you like, take some personal time to physicaly go out in that area and check it out first. Stay out there a while and ask yourself if this place is honestly right for you. You can only find that out by actually being there. You will probably find better land deals just talking to the locals anyways. I almost moved out to arizona wanting to do the same thing. After spending some time down there it became obvious that it was not for me, happy to be back in good old missouri and glad i didnt build down in az.