I was a little surprised by that statistic also, but from searching through the Census Bureau's education webpages, it does seem to be true. The District of Columbia and the fifteen states of
have more than 30% of the 25-year-old and older population with a bachelor's degree or higher. The rest are lower; the lowest percentages are in Arkansas and West Virginia, both of which have less than 20% of the 25-year-old and older population with at least a bachelor's degree.
The Excel spreadsheet for the educational attainments of the 25-year-old and older population for 2006 is here. The education page for year 2006 is here.