This article originally appeared on The Census Project:

Young children had a higher net undercount in the 2010 Census than other age groups — 4.6 percent, a rate that has “tripled since 1980 while the net undercount rates for most other demographic groups have improved,” according to researcher Bill O’Hare of O’Hare Data and Demographic Services LLC. In his latest research brief, O’Hare suggests that the “biggest problem” in counting young children in the 2020 Census is likely to be in the South.

“Of the 100 large counties with the highest net undercount rates for young children” in 2010, he said, “72 are located in the South.” In addition, “the problem is not confined to the large urban centers of the South. The net undercount of young children in the rural South is much higher than the net undercount of young children in rural areas of other regions.”

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O’Hare emphasized that “counting young children accurately in the 2020 Census should be a high priority.”

Read O’Hare’s new research brief: “Counting Young Kids in the 2020 Census: Don’t Overlook the South.”