I imagine there are a good many of us O gaugers in Northeast Ohio and Western Pennsylvania, myself included. I know at least twenty or more, some of whom are part of our Tuesday Train Gang group (informal) over in Western PA. A good number of guys and gals in the Greenville (PA) area, with a club in the rail museum up there. And certainly don't forget the Corner Field Model Railroad Museum and Hobby Store in Middlefield, OH. Look 'em up via a Google search.
And if you get over to Mercer, PA, be sure to stop in to see Dave Minarik at his Mercer Junction Train Shoppe. Go there on just about any Tuesday afternoon and you're apt to see me there as well. It's a short 45-minute drive for me.
In short: There likely is a very large concentration of O gauge hobbyists in the geographic area you mentioned. Probably one of the largest concentrations in the U.S., along with PA-NJ-NY areas.