It Looks Like a Fact. It's an Estimate.

Every market study starts the same way. Pull the population, pull the growth forecast, and build everything else on top of those two numbers.

Nobody questions that first step, because there's no real reason to. The data comes from the US Census, a regional planning agency, or a platform that pulled it from one of those two. It's sourced and footnoted. And honestly? It looks like fact.

But here's what most people never look at. The Census Bureau checks its own count afterward, and it publishes what it finds.

The Census check

After every ten-year count, the Bureau goes back and tests its results. It surveys a fresh sample of households and compares those answers to what the census recorded. Separately, it builds a second population estimate from birth, death, and Medicare records, then checks that against the count too.

For 2020, the two came out close. The count landed about a quarter of a percent below where the check said it should be, near enough to zero that the Bureau called it no meaningful error at all.

Sounds like the data is fine. Then you look state by state.

Right in total, wrong in the details

Fourteen states were off by an amount the Bureau considers real. Six counted too low, eight too high. Rhode Island came in more than 5% over!

The national number looked almost perfect because the misses ran in both directions and cancelled each other out. Which is the whole problem, because nobody underwrites a deal nationally. A count that holds up across the country tells you nothing about whether it holds up in the market you're actually studying.

So why is the Census off?

It misses the kids

Yup. And this is the one that should matter most to anyone in real estate.

The 2020 count missed children under five by about 5.5%, roughly a million kids. Worse than any other age group, and the worst result for young children of any census since 1970. Newborns were off by about 7%.

Not a fluke, either. Children under five are the only age group whose count has gotten worse every single decade since 1980, and the Bureau has been actively trying to fix it the whole time.

So if your project lives or dies on young families, household formation, school-age population, or pediatric demand, that's the exact group the count handles worst. The Bureau's county-level work found it tracks with things like household structure and child poverty, which means the error in your market probably runs in a predictable direction once you know what the market looks like.

And buildings

The check covered housing units too, and the count was off there as well. Several states came in over, New York by almost 4% and New Jersey by 2.5%.

That cuts two ways. If you're sizing up how much competing inventory a market already has, you're working off an inflated number. And because the yearly population estimates are built partly by multiplying housing units by an assumed household size, overstating the buildings quietly overstates the people in them.

Why a small miss becomes a big one

The ten-year count is the foundation for every yearly estimate after it, and each year gets built off the year before. So an error in the foundation doesn't sit still. It rides forward through the whole decade, and then a forecast stretches it another fifteen years. Off by a few percent at the start and you're off by a lot more at the end.

What to do about it

None of this makes the data useless. It's better than nothing. And every Census cycle it gets more accurate. Most of us can't know every market personally, and you have to lean on it. That's fine.

Just make it prove itself.

Find one number somebody counted instead of modeled. Births get filed with the state. Permits and certificates of occupancy get issued by the town. School enrollment gets reported every year. Hold any of those against the official growth figure and you'll know in an hour whether the story holds together.

Look at the ages, not just the total. A town that looks flat overall can be filling up with young families.

Ask the town if they ever challenged their count. One call to the clerk. If they did, the official number and the number the town believes are two different figures.

Then go be there. Drive down to the area. Sit at the intersection at the hours that matter. Ask the planning office what they're actually approving, which is a different question from what's allowed. Ask a local broker what actually rents and for how much.

None of that takes special access. It takes showing up and caring.

The takeaway

The people who build this data are careful. And they even publish their own errors and tell you where the count estimate is weak. The problem isn't them. It's that the number lands on your screen looking like fact.

Clean data feels like knowledge, and it shows up faster than the real thing. Four minutes gets you a sourced projection out to 2040. Finding out whether it's true takes a lot longer, and it's the only part that decides whether your deal works.

Use the numbers. Just don't confuse having them with knowing a market.