A head to head comparison of the Ohio 2012 General Election gives us an idea of the break down of the voters.    

Barack Obama received 2,697,260 (51%) votes, beating Mitt Romney who gained 2,593,780 (49%) by 103,480 votes in Ohio.

Mitt Romney won 72 counties whereas Barack Obama won 16 counties in the total of the 88 counties in the State of Ohio.

Presidential General Elections

During the 2012 General elections, over 122M total number of votes were cast. Barack Obama got 62,614,654 (62.6 Million) over Mitt Romney's 59,141,654 (59.1 Million). He won the popular vote by 3,472,979 (3.4 Million). His victory in the State of Ohio (with 2,697,260 votes) represents 4.1% of his popular vote victory. The remaining 49 states contributed to the remaining 95.9% popular votes victory.

Top 15 Counties in Primary Elections vs General Elections

All Candidates (General Elections)

These 15 counties play an important role in these Primary elections. If a candidate, can get a sizable majority in the larger counties (Cuyahoga, Franklin, Hamilton, Summit), it becomes very difficult to win majorities in the smaller counties without voter outreach and increased voter participation in them.

Top 15 Counties Comparison in Primary Elections vs General Elections

General Elections
Barack Obama

General Elections
Mitt Romney

Cuyahoga, Franklin, Hamilton and Summit, four of the larger counties, voted in favor of Barack Obama giving him a 412k vote advantage. However, Mitt Romney's steady win in the less dense counties (like Butler, Stark, Warren, Medina and more) fell just shy of overcoming that deficit, making Barack Obama gain an upper hand in the State of Ohio.

Related References: 2016 Ohio Primary Election Story, 2016 Ohio General Election Story, 2020 Ohio Primary Election Story, 2020 Ohio General Election Story