New York ? America welcomed its 300 millionth person at 6:46 a.m. CDT Tuesday.

That’s still small potatoes compared with billion-plus giants India and China, which already had more than 300 million people a century ago.

But at least the U.S., which is home to just under 1 in 20 of the 6.6 billion people worldwide, is still growing.

Fueled by economic growth and abundant immigration, America should add 100 million people by the middle of the century.

That will be enough to keep the U.S. in the No. 3 slot on the world’s population chart as Indonesia, the No. 4 nation, plays catchup, according to the International Institute for Applied Systems Analysis, a nongovernmental research organization.

At the other end of the scale is tiny Vatican City, which has a population of just 770.

The U.S. is one of the few Western nations that still is growing. With birthrates plunging, Europe and Russia also are losing people to the tune of about 100 million people in the next half-century, according to the research institute.

Overall, the planet is expected to have about 8 billion people by 2025 and 9.3 billion in 2050, give or take a few.

Almost all of the 80 million or so people being added to the world’s population per year in the next couple of decades will come from developing nations, especially in the South Asian subcontinent and sub-Saharan Africa.

India, blessed or cursed with higher fertility rates, is expected to overtake China somewhere around 2050 and become the world’s most populous nation.

Two of the fastest-growing countries in the next decades will be Nigeria and Pakistan. Both are expected to triple in population by 2050 to about 350 million apiece. They will both pass today’s No. 5 nation, Brazil, which will level off around 250 million people during the middle of the century.