The chart above is from surveys by the Gallup Poll -- the most recent being done between April 1st and 19th of a nationwide sample of 1,018 adults, with a 4 point margin of error.
Between 2002 and 2008 about 61% of Americans said they were in the middle class. Currently, only about 52% say that -- a drop of 9 points. That drop is evident in all demographic groups.