User blog comment:NathanGMan/Phineas and Ferb Live In VIRGINIA?/@comment-169320-20120331171629

Actually, they live in "Danville, USA" of which there are quite a few cities in the United States named Danville. Additionally, there are (according to Wikipedia) forty-eight areas called the "Tri-State Area" of which I live in one of them (the Pennsylvania/New Jersey/Delaware region) and have traveled to the New York/New Jersey/Connecticut region. In the case of P&F, this particular region is closer to the Rocky Mountains.

So, based on that, my final thesis is this: