Ernie, I think that would depend on if you are asking what county has the most coyotes or the county that has the most success in calling. Many counties with the most coyotes also have the highest calling pressure. Counties like York may have few coyotes, but a lot of people don't realize that there are coyotes in York County, therefore the hunting pressure is less.....
For Example: I have a camp in Clinton County. I am always hearing Coyotes going off. However, my calling success is very limited. I think thats mostly due to the amount of hunting and calling pressure up there.
I call mostly in York County. I have actually called in more Coyotes in York County than Clinton County, even though I think there are fewer Yotes in York County. Soooo.....Compareing Clinton County with York County, I would pick York. The most populated area's with the most limited amount of hunting pressure.....Like the outskirts of Pittsburgh and Philly!!
Not sure if this helps, but it might spark come further comments....