Gallup reports that of the 700 some-odd million people who want to permanently emigrate, 165 million of them want to come to the US. That would be a group of people roughly equivalent to 53% of the current US population. Though far fewer people want to move to Singapore, they would see an even larger population increase by percent.
The top ten countries whose people want to move here are:
China - 23 million - 2% of them
India - 17 million - 1.5% of them
Nigeria - 17 million - 11% of them
Ethiopia - 10 million - 13% of them
Bangladesh - 8 million - 5% of them
Brazil - 8 million - 4% of them
Mexico - 6 million - 5.5% of them
Philippines - 6 million - 6.5% of them
Vietnam - 5 million - 6% of them
Japan - 3 million - 2% of them
We let in less than 0.6% that many.
Out of that 165 million, Wiki tells me that a record 1 million became naturalized US citizens in 2008, mostly from Mexico, India, and the Philippines. In 1890, 15 percent of the people living here were foreign-born. "By 1970 immigrants accounted for 4.7 percent of the US population, rising to 6.2 percent in 1980 and to an estimated 12.5 percent today."