As late as yesterday afternoon, organizers of the event expected upwards of a million protestors. Although no "official" estimates are being offered by the National Park Service, the news media is reporting "tens of thousands" of protesters and street level reports from protestors themselves put crowd estimates anywhere from 15K-50K, while reports from the DC Fire Department put the crowd at anywhere from 60K-70K
Event organizers had been planning the march for six months.
To give this some perspective, with only 6 days notice, President Obama's healthcare rally in Minnesota drew capacity crowds. of 15,000+