The United States is the third-most populous.
As of May 27 , 2017 , the United States has a total resident population of 325,120,392 , making it the third most populous country in the world . United States . At 3.8 million square miles ( 9.8 million km2 ) and with over 324 million people , the United States is the world 's third - or fourth-largest country by total area , third-largest by land area , and the third-most populous .