It is illegal to release information that would identify individuals or families.

But that does not mean that census data has not been used to target specific populations in the past.

In fact, information from the 1940 Census was secretly used in one of the worst violations of constitutional rights in U.S. history: the internment of Japanese Americans during World War II.

…Even lawful disclosures can raise alarms. The Census Bureau came under scrutiny in the years after the Sept. 11, 2001, attacks, when the bureau gave publicly available information to the Department of Homeland Security about neighborhoods that were home to large numbers of Arab Americans.

Secret use of census info helped send Japanese Americans to internment camps in WWII – The Washington Post

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