If Facebook were a country, it would be the THIRD LARGEST country in the world, BIGGER than the U.S. and Indonesia.
In 2009, Facebook CEO Mark Zuckerberg announced that Facebook had 200 million users, which (if Facebook was a country) would make it the fifth largest in the world.
That was back then. Now, Facebook's statistics page claims that there are more than 400 million active users (twice as many as last year!). This means that there are more Facebook users than people living in the United States (309 million) or Indonesia (231 million). The only countries with bigger populations than Facebook are China and India.
(Sources 1, 2, 3, 4)