>The US is fast growing in population.

No.

Google: 'US births per woman'. In the US, that is ~1.7. 2.1 is considered the replacement rate in developed countries.

After that, check out: 'world births per woman' Currently (2011) @ 2.41 down from 2.67 in 2000, 3.23 in 1990. Do you expect this trend to suddenly flatten or reverse?

In the future, longer life expectancy will likely have a larger impact on population numbers than birth rates. In specific developed countries, I would also expect immigration to be part a large part of growth.