NEW YORK — As a teenager, tennis legend Althea Gibson played paddle tennis on the streets of her New York City neighborhood.

But there's no record of Gibson or her parents in the 1940 U.S. Census. They're among the estimated more than 1 million blacks who never made it into the count.

There was an undercount of nonblacks as well, but the percentage wasn't as high.

Undercounts in the census can have impacts on everything from the configuration of congressional districts to the distribution of federal dollars.

The 1940 undercount had an impact on the Census Bureau itself, leading to efforts that continue to this day to count every single American.

The census was long known to have missed millions of people. But genealogists digging into recently released records may be rediscovering it.