A census is an enumeration, or counting, of a population. The information from a census is used to help governments determine where to provide services, based on the demographics of the population. Information about age, gender, number of children, race, languages spoken, education, commuting distance, salary, and other demographic variables is common in a census. This information is compiled and provided to government agencies and is usually accessible to the general public.

In the United States and most other developed nations, a census takes place once every decade. The Constitution of the United States requires a census to be taken every 10 years, in order to create districts and determine the number of members of Congress each state is able to send to the House of Representatives.