The County is the extension of the State government. So I assume you would start by A)researching the topic on the State level(such as your State's Constitution) B)start talking to the State Representatives of those two Counties. To be honest I don't you can do this.
FWIW, I think the red bits of Upstate need a new state. We could take some of the red bits of PA along with us, too. I think that might be even better than switching counties.