http://nces.ed.gov/naal/kf_demographics.asp
Go down to Number of Adults in Each Prose Literacy Level. The numbers are broken down into Below Basic, Basic, Intermediate and Proficient.
14%(BB), 29%(B), 44%(I), 13%(P) corresponding to 30 million, 63 million. 95 million, 28 million.
The top notes, No Significant change between 1992 and 2003
There are all sorts of interesting stats on education that might be useful for public ed advocates.