What public event had the largest attendance of any event in the history of Washington, DC?

The Swearing In Ceremony for President Barack H. Obama at the Fifty Sixth Presidential Inaugural Ceremonies on January 20, 2009 had the largest attendance of any event in the history of Washington, DC, and it had the largest attendance of any Presidential Inauguration in U.S. history. It is believed that about 1.8 million people attended the inauguration (about one third of the population of Ireland gathered in one expansive public area). Additionally, based on the combined attendance numbers, television viewership and Internet traffic, it was one of the most observed events ever witnessed by the world audience.

The Presidential Inauguration of 2009 took place as the nation prepared to celebrate the 200th anniversary of Abraham Lincoln’s birth. The President elect took the oath of office and addressed the nation from the West Front of the United States Capitol, looking across the National Mall toward the Lincoln Memorial, where many of the sixteenth President’s immortal words are inscribed. Although some inaugural traditions have changed since Lincoln’s time, the swearing in ceremony continues to symbolize the ideals of renewal, continuity, and unity that he so often expressed.