Ohio could well decide the next president.
The state has chosen the winner in the last 12 presidential elections, and it's pivotal to the strategies of both President Barack Obama and Mitt Romney.
The Ohio winner has usually done particularly well in his party's traditionally strong areas, and better than expected in other regions.
The state's geography is often divided regionally as the "Five Ohios" - the northeast, northwest, central, southeast and southwest parts of the state.
Obama needs to pile up votes in northeast Ohio, the state's Democratic stronghold, anchored by Cleveland and the industrial towns of Youngstown and Akron.
Romney seeks big numbers in southwest Ohio, where the conservative suburban crescent around Cincinnati is Republican turf.