U.S. Population Tops 309 Million (We Think…)

by Mark Mather, associate vice president, Domestic Programs

With the 2010 Census enumeration winding down, we demographers are getting excited about data. The census happens just once every 10 years and no one knows exactly what the results are going to show. If the Census Bureau’s latest population estimates correctly foretell the 2010 Census count, then the official tally for April 2010 should come in around 309 million. 

But there’s a lot of wiggle room around that number, and the final count could come in several million people higher or lower than we expect. Back in 2000, the official census tally, at 281.4 million, was nearly 7 million people higher than expected based on intercensal population estimates. That’s like missing the entire population of Arizona. 

Why is there so much uncertainty? After all, the population balancing equation is pretty straightforward: Just add births, subtract deaths, and add net international migrants (immigrants minus emigrants) to last year’s population to get the population for the current year. 

One of the challenges is getting reliable estimates of net international migration. Immigrants are a diverse population, consisting of legal immigrants, refugees, unauthorized migrants, temporary migrants (such as students or temporary workers), and migrants from Puerto Rico (see the table here for more detail). Of these groups, unauthorized migrants are by far the most difficult to track, and their migration flows can change in response to short-term social, economic, or political factors. The Migration Policy Institute has linked a decline in unauthorized immigrants to the recent recession, but we do not have any hard numbers on this trend. 

Here is another challenge:  U.S. population estimates are only as good as the decennial census counts on which they are based. You can think of annual estimates as hands on a clock. Every 10 years we reset the clock to the “correct” time based on the decennial census enumeration. Then, over the next 10 years, we move the hands of the clock forward (or backward) based on the estimated numbers of births, deaths, and net international migrants. Part of the challenge is setting the hands to move at the right speed. But arriving at the correct time in 2010 also assumes that we set the clock to the right time back in 2000. In many ways, the 2000 Census was considered to be one of the most accurate in history, but there were still millions of people who were missed and millions more who were counted twice. To the extent that the Census Bureau corrects these erroneous omissions and duplicates in 2010, the population could come in significantly higher or lower than expected. 

The first official national and state population counts from the 2010 Census, which are used to apportion seats in the U.S. House of Representatives, must be delivered to the President of the United States by December 31 of this year. What will the data show? I’m going to put the U.S. population as of April 1, 2010 somewhere between 304 million and 314 million. And if I had to pinpoint a number, I’d put the final tally at around 307 million, slightly below the Census Bureau’s current estimate. What do you think the official count will be?

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