You can pay the registration in any county office. I live in canyon county and usually go to the dmv in Boise. My registration still says canyon county
You can register anywhere. Although, from experience, if your not renewing and it's a brand new registration you will get that county's plates. Living in Ada I registered in canyon and received 2C plates. I've RENEWED other vehicles and kept my A1, but brand new issues get plates from whatever county your in apparently.
It has to be registered in the county you live in
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