“The population of the United States will pass 300 million today, or
tomorrow. No one knows exactly where, no one know precisely when.”

”
It was in 1915 that the US population reached 100 million. Fifty-two years
later, in 1967, it reached 200 million. It has taken just 39 more years for
the milestone of 300 million to be achieved.”

Both quotes from the artice here
http://news.independent.co.uk/world/americas/article1834360.ece

According to a 2005 Wikkipedia article, the US is the third largest country by population, behind India in second place, and China in first place.  Read the wikkipedia article here
http://en.wikipedia.org/wiki/List_of_countries_by_population

According to the International Programs Center, U.S. Bureau of the Census, the total population of the World, projected to 10/12/06
at 02:19 GMT
(EST+5) is

6,549,826,668