If you were asked on a quiz show, you might know that the two countries with the largest populations in the world are China and India. But could you name the remaining countries in the top 10? And do you know which countries are expected to join the top 10 in the coming decades?

Answers can be found in the U.S. Census Bureau’s International Data Base (IDB). This leading source of demographic information on the Web is being updated today. Projections of country populations are based on assumed changes in births, deaths, and migration — information that is also available on the IDB.

The United States is currently the third most populous country in the world and is projected to remain so through 2050. In contrast, the rankings of other countries in the top 10 are expected to change. For instance, Russia and Japan are projected to drop out of this group by 2025 due to persistent low fertility, which has already caused their populations to decline. Also, by 2025 India is expected to overtake China as the world’s most populous country (see graph below). But in the future, countries with high fertility, such as Ethiopia and Nigeria, are likely to advance in the rankings.

If you are interested in countries with smaller populations, the IDB provides information about them too. The IDB provides estimates and projections for 228 countries and areas that have a population of at least 5,000 people.

Two new countries or areas are being added to the IDB with this update — Curacao and Sint Maarten — and one is being removed — Netherlands Antilles. The Netherlands Antilles dissolved on October 10, 2010. Curacao and Sint Maarten (the Dutch two-fifths of the island of Saint Martin) became autonomous territories of the Kingdom of the Netherlands. Bonaire, Saba, and Saint Eustatius, the other islands of the former Netherlands Antilles, now fall under the direct administration of the Netherlands.

Students, researchers, international organizations, governments, planners, businesses, and quiz show aficionados find international data on population to be extremely useful. The IDB is a very popular demographic resource, receiving nearly 400,000 hits per month.

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