Romney will carry Hamilton (Cincinnati), Franklin (Columbus), Cuyahoga (Cleveland), and Montgomery (Dayton) County, and likely Delaware County, too. Santorum will carry most of the other 83 counties in Ohio. The margin in those cities matter, but I suspect Romney will win the popular vote by 2% to 3%.
Santorum
37.6%
361,976
Romney
37.3%
359,171