The strong culture of confidentiality at the Census Bureau has grown and evolved over time, shaped by a growing sense of a right to privacy among the people of the United States. The final result of this build-up is the confidentiality protections that are codified in Title 13 of U.S. Code, the rules governing Census Bureau activity today.
This was not always the case. Early census questionnaires were public; the authorizing legislation for the 1790 census actually required that they be posted in a public place so that people could check the accuracy of their entry. Throughout the nineteenth century, the director of the census was informally entrusted with ensuring the confidentiality of both companies and individuals responding to the survey, but by the early twentieth century, presidential proclamations formally recognized the need for privacy.
During World War I and World War II, changes in federal law led to the roll-back of many protections on Census Bureau data. After each war, these privacy protections were restored.
The Census Bureau produced a monograph on Privacy and Confidentiality [PDF 1.61 MB] in July 2001.
For a chronologically arranged table, see Events in the Chronological Development of Privacy and Confidentiality at the U.S. Census Bureau. [PDF 680 KB]