Where have all the people gone?

When the U.S. Census Bureau reported its 2010 population findings last month, it said it had counted 420,003 people in the city of Atlanta.

That’s 3,529 more people than the Census found in Atlanta in 2000.

But it’s 117,955 fewer people than the Census Bureau’s own estimate of Atlanta’s population in 2008.

“The Atlanta count for 2010 was quite a bit lower than our estimate,” Census spokesman Robert Bernstein admitted.

That’s a bit of an understatement.

“The numbers that were put out were really surprising,” said Reese McCranie, the city’s deputy director of communications.

What happened? Revisions of the 2000 count due to challenges from the city and Fulton County led the census to project a number that was too high, Bernstein said.

“It was an overestimation,” he said.

Fulton County challenged its population estimate in 2004 and the Census agreed to raise the Fulton County number to 905,802, Bernstein wrote. (The 2010 Census recorded 920,581 people in Fulton County.) As most of Atlanta lies within Fulton County, Atlanta’s population estimate rose along with the county’s in 2004.

Then, Atlanta challenged its 2005 estimate and the number again was raised, Bernstein said.

The problem was that some of the Census’ assumptions were off. “These challenges were based on housing unit data provided by the city and county and population per household (PPH) and vacancy rates from Census 2000,” Bernstein wrote in an e-mail.

But the city’s vacancy rate rose from about 10 percent to nearly 18 percent during the decade, he said, and the population per household rate dropped from 2.3 in 2000 to 2.1 in 2010. That translates into fewer people.

Atlanta city officials have until June 1 to decide whether to challenge the 2010 population count, Bernstein said. McCranie said city officials likely will decide within the next 30 to 45 days whether to mount a challenge. The decision will be made by Mayor Kasim Reed, he said.

“It’s something we’re reviewing thoroughly,” he said. “We’re reviewing the numbers and we’re looking to see whether cities are.”

Federal and city officials often say the Census figures are significant because they are used to determine everything from a community’s political representation to the amounts awarded in federal grants and other revenues.

“It matters that the number is accurate,” McCranie said. “We’re looking to see if that number is indeed accurate. It’s important for a whole host of reasons.”

So city officials are thinking about whether they should once again take on the Census in an effort to raise the city’s official population estimate.

“The numbers they are providing are 120,000 less,” McCranie said. “That seems wildly off.”

Joe Earle is Editor-at-Large. He has more than 30-years of experience with daily newspapers, including the Atlanta Journal-Constitution and was Managing Editor of Reporter Newspapers.