(Image source- 2010 Census website)
Here's two little-known anecdotes of times that people have tried- and failed- to access confidential Census data.
1953— During the Truman administration, the White House had to undergo renovation. It was necessary to relocate the President until the renovation was completed. The Secret Service requested from the Census Bureau information on residents living in the proposed relocation area for the purpose of performing background checks. However, because census data are ABSOLUTELY CONFIDENTIAL, even to the President, the request was denied. President Truman spent his exile at Blair House.
1980—Armed with a search warrant authorizing them to seize census documents, four FBI agents entered the Census Bureau’s Colorado Springs office. No confidential information was ever released because a census worker held off the agents until her superiors resolved the issue with the FBI.
Another little known fact: in 1961, Congress strengthened the law so that even copies of census questionnaires kept in your possession cannot be used as evidence against you in a court of law.
Want it spelled out more simply? As one Census administrator put it:
"No one can get access to census data. It is rock solid secure."
--James T. Christy, Los Angeles Regional Census Office Director
Complete Count Committee guide - Census Bureau