It was a Census number that no one saw coming: Despite years of rapid growth, D.C.’s 2020 population came in a good 23,000 people lower than expected.

Questions rippled across social media the day the Census Bureau released its decennial apportionment numbers last week. How could D.C.’s population be 689,545, when officials have been saying for years that the city had crested 700,000? Was there an undercount? Is D.C. going to lose federal funding? How will ANCs and ward boundaries be affected? What about the baby that Mayor Muriel Bowser anointed the city’s 700,000th resident? Should we tell the now three-year-old?

To answer (some of) these questions, DCist/WAMU turned to one of the nation’s top experts on the Census: Andrew Reamer, a research professor at George Washington University. Reamer studies U.S. economic development and competitiveness, and a big part of his work focuses on the relationship between the Census and federal funding to the states and D.C.

At this point, it’s hard to predict exactly how the 2020 Census numbers will affect D.C., politically and fiscally, Reamer says. There are a lot of unknowns and complicating factors. We’ll know much more this fall, after the Census releases its next round of data — those numbers will zero in on characteristics of the population, such as race, income, ethnicity, and housing occupancy status. That information usually has a greater impact on federal funding than the apportionment numbers, Reamer says.

But we can still make some educated guesses about how D.C. will be affected by the new population count.

First of all, why should D.C. (or anyone) care about the decennial Census?

“The accuracy of the Census drives how well our nation functions,” Reamer says. “Democracy couldn’t operate without the Census, and that’s why the Census was created.”

One of the most important functions of the Census is determining states’ representation in Congress. (For D.C., that’s easy: it has no voting representation.) But it’s also important for determining political boundaries in a non-state like D.C. The city redraws its ward boundaries every 10 years based on the decennial Census, and that also affects the makeup of ANCs, the elected bodies that represent District residents on the neighborhood level.

Businesses also run on Census data, Reamer says. “I live in Cleveland Park, and there’s a Target up the street from me,” Reamer says. “There’s also a Target in Columbia Heights. But they don’t carry the same inventory of goods, because Target knows from Census data that people who live in Columbia Heights are going to buy some things that are different from people who live in Cleveland Park.”

The decennial Census also shapes the annual population estimates and other data that the Census tabulates every year. The annual American Community Survey, which collects detailed information about certain neighborhoods across the country, depends on the count that the Census Bureau conducts once each decade.

“Every year, the Census bureau updates its population estimates for D.C., and they’ll take the 2020 number and add births, subtract deaths, and estimate migration, to get a net,” Reamer says. “The accuracy of these numbers depend on the accuracy of the 2020 Census. Which is to say, you screw up the 2020 Census, and you screw up the American Community Survey.”

And yes, the Census has major implications for federal funds the city receives annually for things like health care and education. Here’s more about that.

Could D.C. lose federal funding, thanks to the smaller-than-expected population count?

“Yes, D.C. will lose money,” Reamer says. “The question is how much money.”

Most federal programs allocate funds based on D.C.’s share of a population with particular characteristics, not just its overall population. For example, D.C. receives a lot of federal funding for schools. But the amount is based on D.C.’s share of children in poverty who are between the ages of 5 and 17, not the entire population.

“I don’t fill out the Census form, D.C. doesn’t lose a penny because I’m not poor and a child,” Reamer says.

If the Census Bureau undercounted the number of children in D.C. who live in poverty — which could easily happen, Reamer notes — that could lower the amount of federal school funding the city receives. But we don’t know who, if anyone, was undercounted, so there’s no simple way to calculate how that could affect funding.

It’s also possible that D.C. received more than its fair share of funding in previous years, based on annual population estimates that might have been higher than they should have been. The District benefits when its population is overcounted.

“The more people you have as a share of the nation, the more money you get,” Reamer says.

So… did the Census undercount D.C. residents in 2020?

Possibly! That was officials’ greatest concern in the lead-up to the 2020 Census. President Donald Trump tried unsuccessfully to add a question about citizenship to the survey, which likely discouraged a lot of immigrants from filling out a form. Then there was the pandemic, which seriously complicated how the count was conducted.

But there are a few scenarios that could have led to the surprising population count, Reamer says — and all of them could be true simultaneously.

• There was an undercount in 2020. “We still don’t know enough about how the pandemic and how the political stuff — Trump’s call for a citizenship question, his call to exclude non-citizens from the Census — may have affected the count,” Reamer says. College students could have been missed, too. That’s a concern in college towns across the country, the professor says. “Places like Amherst, Massachusetts, and Ames, Iowa, have been freaked out because all the people that were supposed to be there April 1, 2020, went home. So it’s very possible that somehow, despite the best efforts of the Census Bureau, D.C. got undercounted because a lot of college students went home.”
• The Census could have gotten the previous years’ estimates wrong. It’s not hard for the government to miscount domestic and international migration, for example. Maybe when the Census pulled IRS records to fill in gaps in the count, the number of exemptions a person puts on a form doesn’t actually correspond to the number of children living in their home. Then there’s international migration, which can be distorted by undocumented immigrants who don’t complete the Census or are otherwise hard to count, Reamer says.
• There could have been problems with the math. The Census estimates that it undercounted D.C.’s population by about 2.25% in 2010, due to a combination of undercounting and overcounting, Reamer says. When the government tried to correct for that in 2020 by using administrative records to fill in gaps, it could have eliminated people who might have been counted twice, while undercounting people who didn’t show up in the records. The Census is extremely sophisticated, Reamer says, but it’s still a work in progress. “If you look under the hood of the Census, it’s very messy,” the professor says. “Still, every Census gets better than the last one.”

What happens next?

The Census works on verifying their count. The bureau usually runs two types of analyses to check the accuracy of their numbers, Reamer says. First, they use administrative records to double-check the count. Then they run what are called Post-Enumeration Surveys in particular places, “with a level of effort that would bankrupt the country if they did it for every neighborhood,” Reamer says.

Communities can also appeal their numbers, which D.C. may opt to do, if it can. Census wonks like Reamer are paying close attention to possible changes to the grounds for appeal, which in the past have been very narrow, but could change this year.

Finally, Congress could require the Census to make adjustments for the purposes of calculating federal funding, but Reamer doesn’t seem to think that’s likely. Any change in the count has winners and losers, he explains. The bigger a state’s share of the population, the more money it gets. So when D.C.’s count came in below what the estimate was, “every other state was a winner, because every other state’s share of the population went up microscopically.”

In other words: Other states might like the outcome, and not want to muck it up for themselves.

So is D.C. getting its fair share of federal dollars? Reamer says that’s a question that only time — and careful calculations — will answer.