Regarding literacy rates. That figure seems to mesh up with wwhat I have founf online for the literacy rate at the time.
Remember in the pre civil war period immigration was a relative trickle compared to what it would become and most of those immigrants were from western european nations where there were school systems generally in place.
I also suspect that not just English literacy would have been counted. At the time most non English speaking immigrants were German, and if historical documentation is accurate, literacy in that part of society was virtually 100 percent.
Literacy rates in the South are FAR lower, largely I suspect due to the large black populations. That remained an issue in the South for over 100 years.
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