Passing by all the local chain chili joints, it's easy to see that chili is a big deal in Cincinnati - a VERY big deal.
But if you want the real deal, make your way to 'PRC'. This is a very popular spot with the locals (much more so when the bars let out) and the cheese and gravy fries are a particularly big draw.
And if you're not local, study up on how to order your Cincy chili, which comes on top of spaghetti. Know your way around the 3-Way, the 4-Way, wet and dry, etc. By the way, a 'Coney' is a chili dog with cheese on it.
(A warning to vegetarians: while the other chili joints in town almost always have a veggie chili available, PRC doesn't. If you come, you might be stuck with just plain fries.)