Why is Indiana so damned Republican?

[Bleeding heart conservative, HTMLdon]

The rural areas are definitely the reason.  More than 70% of Indiana's counties have less than 50,000 people (Group A), and more than 80% have less than 100,000 (Group B).  Group A counties make up 30% of Indiana's population and Group B makes up an astounding 41% of Indiana's population.  Given the fact the rural voters come out in higher numbers than urban voters, it becomes clearer why the state has such strong Republican trends.

That makes sense in current terms, but why were they so strongly Republican back when Republicans were seen as the party of elitist north-eastern Business interests and Democrats were seen as the rural farmer's party?

That's not quite the way it was.  Yes the GOP had the business interests but also dominated virtually every rural area in the north and midwest.  The Democrats just had the rural south.