There's no record of tennis champ Althea Gibson in the 1940census. (Keystone/Getty Images)

CBS is reporting today that more than a million black people were unaccounted for by the 1940 census. Why does that matter all these years later? The mistake reportedly affected everything from the political map to the distribution of resources. And while the undercount estimate has generally gone down, it's still disproportionately high for blacks compared with nonblacks.

CBS News reports:

There are a variety of reasons for undercounts — people move around; people may not know or be reluctant to answer government questions; address lists may be inaccurate; extremely crowded areas can be difficult to count, as can extremely isolated areas. Experts believe some of those factors weigh more heavily on minority undercounts, particularly the challenges of counting in urban areas.

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The 1940 census was long known to have a black undercount. Evidence of it was found within a decade in a demographic study of young children and another of draft-age men. But modern-day genealogists digging into the newly released 1940 census records may be rediscovering it when they cannot locate their relatives or friends …

The importance of an accurate count is vital, since the data is used in a number of ways. That includes the main purpose, written into the U.S. Constitution, that Congressional districts are apportioned by the census population counts. But it also matters because federal dollars flow to states and localities based on that effort, meaning a wrong count in a census year can impact a whole decade.

"It literally can mean the difference of tens of millions, hundreds of millions, of dollars,"[Phil] Sparks [former associate director of the bureau and now co-director of The Census Project] said.

Read more at CBS News.