Per

"U.S. Department of Commerce, Bureau of the Census, Historical Statistics of the United States, Colonial Times to 1970; and Current Population Reports, Series P-23, Ancestry and Language in the United States: November 1979. (This table was prepared in September 1992.)"

In 1910 only 7.7% of people over age 14 in the united states were illiterate. , note the discrepancy by skin color, definitely seeing a correlation netween increased school enrollment and literacy (showing up is half the battle!)

I recall in "amusing ourselves to death" neil postman alluded to the fact that our literacy rates actually dropped from the late 1700's but I couldnt find a reliable source to back the claim