Hamilton and Sandusky counties are identified by Axiom as their “bellwether” counties in Ohio, but maybe Ottawa is too, if you beleive that part trends are valid indicators in this election cycle.
There’s been no recent polling, but it’s worth keeping an eye on these counties:
http://axiomstrategies.com/abc/
But as always, “garbage in, garbage out” and while Axiom can be 100% accurate in knowing how these counties voted in past elections, their polling methods, weightings, and analysis should be viewed as critically as any other.
There is no bellwether county in Ohio, especially this year. Trump will vastly exceed Romney's margins in formerly strong Obama counties, like Mahoning and Trumbull, but will likely underperform in the GOP suburbs of Cincinnati (Warren, Butler, and Clermont). His margins in very strong but sparsely populated counties, like Putnam, Mercer, and Van Wert, will be much better than Romney achieved, but there are fewer votes there.
Perhaps the county that will come close to the statewide average this time around is Montgomery, the old stomping grounds of LS.
Trump needs about 500,000 votes out of the remainder of the state to offset the big tallies The Harridan will rack up in Cleveland, Columbus, and Toledo.
My guess as of today is that Trump wins Ohio by one to two points, Portman crushes Strickland, and all of the House incumbents win.