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

Mitt Romney received 1,412,620 (55%) votes, beating Barack Obama who gained 1,140,420 (45%) by 272,200 votes in Indiana.

Mitt Romney won 83 counties whereas Barack Obama won 9 counties in the total of the 92 counties in the State of Indiana.

Presidential General Elections

During the 2016 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). Even though he lost to Mitt Romney in the State of Indiana, his 1,140,420 gained votes represents 1.8% of his popular vote victory. The remaining 49 states contributed to the remaining 98.2% 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 largest counties (Marion, Lake, Allen, Hamilton), it becomes very difficult to win majorities in the smaller counties without voter outreach and increased voter participation in them. However, steady win margins in less popular counties can amount the marginal win to get the entire State. (As in the case of Mitt Romney in the State of Indiana).

Top 15 Counties Comparison in Primary Elections vs General Elections

General Elections
Barack Obama

General Elections
Mitt Romney

Marion and Lake, two of the larger counties, voted in favor of Barack Obama giving him a 141K vote advantage. On the other hand, Allen and Hamilton, other larger counties, voted in favor of Mitt Romney giving him a 71K voter advantage, which on itself was not enough to overcome that deficit. However, steady marginal wins for Mitt Romney in the less popular counties gave him an upper hand in the State of Indiana.

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