Highland Park Illinois
According the the cia.gov website, the total US poplulation over the age of 15 who can read and write is 99%. That may seem quite high, but since the US population is approximately 312.8 million that still leaves over 3 million illiterate citizens.
If you think about it, the concept of willingly spending time in the woods is a strange one. Evolved civilization began erecting buildings, shelter, and advancing technology, to get away from the hardships of living on the land. As civilization progressed, and people began to distinguish themselves more and more from nature, there was less of a need to spend time in the wilderness and even outside proper.