21% of individuals identifying as Italian-Americans speak Italian fluently, as of the last US Census surveys from 2013 to 2017.

That’s around 3.4 million people. Not counting those who speak regional dialects very well but not Italian and all those Italian permanent residents/immigrants and citizens who didn’t care (or couldn’t in case of some immigrant classes) to fill out the Census form to begin with. So that % is in the negative.

Remember that early Italian immigrants (1870’s — 1930’s) didn’t speak Italian at all. Which is why the 1970’s — 1980’s where the decades when Italian reached its peaked diffusion in America. The majority of them received basic education.