These documents refer to the decennial census conducted in the 50 U.S. states, Washington D.C., and Puerto Rico.

Technical documents are designed to help people use published statistics. The resources available for download may vary by census year and can include the following. 

Codebooks - Information about the files, including descriptive information on all of the variables.

Data Dictionary - A repository of information describing database attributes including identification of record codes and area characteristics, endnotes, and table section.

Historical Changes - Information for the current census year and prior census years.

Methodology - The methods we use to collect census data and produce the census results, including sampling, questions, collection, review, quality, weighting, etc.

Questionnaires - Find the most recent questionnaire and whether an archive of past questionnaires is available online.

Subject Definitions - Definitions of population, housing and other variables to help you understand the results of a census.

User Notes - Issues affecting the census, including design, collection, processing, tabulation, and release, to be better informed when analyzing stats.