The population of the United States is forecasted to grow 9.9% from the 2000 Census of 281,421,906 to 309,162,581(Wikipedia article on the population of the USA.)
The size of the USA’s land area according to the CIA World Factbook is 9,161,966 sq km.
So if everyone in the USA were to mark off a 1.5 m square on the ground they would take up 463.75 sq km. That means only 0.000051% of the area would be used leaving the other 99.999949% or 9,161,502.25 sq km uninhabited.
Now we open GIMP and do some fancy foot work.
This graphic (click it) represents what the population takes up and what would be uninhabited. Do you see that little red dot in the top left corner? That’s us.