According to this 2009 USA Today article http://www.usatoday.com/news/washington/2009-01-19-crowd_N.htm
A crowd that fills the space between the Lincoln Memorial and the Washington Monument would number MORE than One Million people. In fact, according to USA Today that space would hold 1.5 MILLION people. Now look at the overhead photo below and you tell me if there were 1 million people in attendance? Remember the rally extended PAST the Washington Monument and BOTH sides of the pond were packed BEYOND both rows of trees.