Yes, plenty of them. During WWII when they tested recruits something like 1/3 of them lacked basic literacy. It's probably better these days, but don't assume just everyone figures it out.
I have no other way to describe the type of language I saw. Everything from no punctuation, incorrect grammar, run-on sentences, slang. Sentences that just seem to be stuck together, whether due to missing punctuation or something else I don't know. Oh, and that was when their point was valid/related.
These individuals got degrees.
No school bus, no weather radar, not necessarily even enough food. The school lunch program was founded (partly) because so many of those WWII recruits were malnourished.
I think that stat is more of a testament to how far the U.S. has come.