If you’re creating a fictional town and sheriff, why not just create a fictional county? Not quite sure what the issue is here.

If you do go with a real county, and down the road there is some sort of issue, I’m sure all you’d have to do is change it and problem solved.

Happy writing.

I wouldn't worry about it at all unless you're writing a "based on" or "true story", then the actual people might take issue with it. It's your job as a writer to tell a great story, any issues with other stuff are the filmmaker's problem. IMHO.

THere are a zillion scripts with fictional characters in real towns/counties. I don't see an issue here either way

Yes, do that. Create fictional everything! There's a fictional country in the Tom Hank's movie The Terminal. Why not county then. Screenwriters are kings of their fiction! yey

As already stated, there are tons of movies and shows that involve fictional characters in real world settings, real world people in fictional settings, or even fictional characters interacting with real world people.

But once any fictional element is introduced, it renders the whole thing fictional. Call it fiction by association. To wit:

New York is real, but there is no Avengers Tower in New York, which makes that a fictional version of New York.

Bruce Lee never had his ass handed to him by a stunt man who looks like Brad Pitt.

Desi Arnaz looks nothing like Javier Bardem.

Donald Trump isn't really a professional wrestler (though he is a professional asshole).

Netflix's adaptation of the tell-all Motley Crue book "The Dirt" rearranges events and includes interactions between people which never occurred in order to fit a film narrative, which renders the entire thing, despite being based on real people and real events, a complete work of fiction.

Brass tacks: write whatever you want to write, set it wherever you want to set it, include whoever you want to include. It's all going to ultimately be fictional anyway.