A census is a complete listing of a population, and it may contain additional metadata about that population. The most commonly referenced census in the United States is the one conducted every 10 years by the federal government. The additional demographic data captured by the census varies from decade to decade, and may be useful to researchers; after 72 years, census records become available to the public though the National Archives and Records Administration as well as sites like Family Search and Ancestry.

Cities, states, and other organizations may conduct a census as well and this may happen once, intermittently, or at regular intervals. Censuses can even be conducted on non-human populations.