That’s shockingly high.
As somebody that has been literate for decades, I can’t even fathom how you would survive. Or if that’s taken care of, how would you entertain yourself?
Although I assume illiteracy indirectly implies that you can speak the language in some acceptable form, I would imagine it would be similar to living in another country without knowing the language. You go into the McDonald's click on the pictures of the food you want, press the big green button, then use your plastic card.
And note that very few counties in the US have a score above 276, which is the top of the range described as "Respondents can paraphrase or make low-level inferences."