Bryan,
Perhaps part of the choice of the midwestern sites was logistics. Another consideration was that Maryland for one would have a milder climate. I know that most of the boys who gave up the ghost at Camp Butler died of pneumonia and other such diseases. I would think that Alton, Rock Island the ones in Ohio and the other Great Lakes states would be almost unbearable in winter. Try Chicago (Camp Douglas) in the winter. It was on Lake Michigan you know (Near Great Lakes NTC is located).
IF the thread does not get to long, maybe we can stay here for the time being.
Frank