How come Indiana is so much more Republican than all the other Midwest states? Are there more Southern descendents there?
I don't know... I'm from NC. :o)
Indiana has always been very conservative (indeed, our governor even refused to call our state legislature for the entire duration of the Civil War--in the process running the state government out of his own pocket--for fear that the state legislature would vote to secede), but for a serious answer to your question, I believe it has to do with the fact that Indiana does not have many big cities.
If you look at the other Midwestern states around us, they are all fairly conservative places, but the big cities "cancel" out the votes of the conservatives. Central and Southern IL are pretty conservative, but you have the massive population of Chicago that swings IL to the democratic side. Same with Ohio. Same with Michigan. But look to Kentucky, without any bigger cities, and you have conservativism.
All that aside, though, as a native and (former) 22 year resident of Indiana, I can tell you that it ain't all that conservative.