I think they meant a quarter of the population being illiterate, that is, that fact that such a statistic exists, is “fucking nuts,” not the illiterate population themselves.
This basically comes down to how you define literacy.
Nationally, 21% of Americans have level 1 or below literacy on the PIAAC literacy scale. That's probably where the 85 people came from.
12% are at level 1, meaning they can only read at a basic level. 4% are functionally illiterate, and 4% had some kind of cognitive or physical handicap or language barrier that kept them from being surveyed.
About 34% of illiterate Americans were born outside the US, so they're possibly literature in another language.
This video is a great discussion of literacy. To put that rate into context, 'illiterate' often includes people that can read and write a little bit, but still struggle with some vital or everyday tasks. According to Wikipedia, 20% of US adults have a literacy level at or below level 1 which would be 80 people in this example. This report has a ton of stats and also defines each level of literacy.
I have no idea how no one has picked up on this and have all decided "Americans are dumb".
What everyone has missed is the literacy statistic is for ENGLISH literacy. The other 20% or so are pretty much all immigrants that cannot speak English and there aren't tens of millions of adults with the mental capacity of a rock.
I’m from Connecticut. Willimantic area, not Greenwich area, but we were still less damaged by Jim Crow and similar policies (except for redlining, that fucked everyone). I spoke to a man in 2017, who had been born in the US, seemed aware and thoughtful, and had to get his granddaughter to write down the claim number I wanted to give him, because he didn’t know his numbers or letters.
I didn’t ask, even though it was killing me with curiosity. His granddaughter probably heard the curiosity in my voice, and explained that in 1967, when he was able to leave school, the teachers didn’t care whether a black kid learned to read. They let him leave school at twelve, even though it was well after brown v the board of education. By the time he wanted to learn to read, he was older, had full time work, and it just didn’t click.
That man was underserved by his government well past the point of mistreatment, not stupid. He’s obviously only one data point, but he’s not the only black man who was treated differently in schools
Only about a quarter of them were born in another country. Then you've got e.g. people with severe cognitive delays or some kind of physical impairment such as blindness. And there's also people whose education system failed them.