How much styrofoam is used in the US each year?

a lot...

Yes a lot is right. In fact according to the American Chemical Council as of May 31, 2011 a year-to-date comparison showed that 1,885,200,000 pounds of Polystyrene-PS was produced, with a captive use of 1,862,200,000 pounds. California is the leading producer of Expanded Polystyrene-EPS, [also known as Styrofoam] generating more than 350,000,000 pounds in 2011.