Every ten years, the United States counts its residents. The census is a systematic count of a population, usually recording age, sex, household composition, and sometimes income, race, and housing. Governments use it to allocate seats in legislatures, distribute funding, and plan public services. Businesses use it to decide where to open stores.

The first modern censuses date to the 18th century in Scandinavia and the United States. Earlier societies conducted counts for taxation or military conscription. Today, national statistical offices run censuses, and the United Nations provides guidelines. Some countries use registers instead of door-to-door surveys.

Why it matters

• Political representation: seats in parliament or congress
• Funding: schools, hospitals, roads, and social programs
• Research: demographic trends, migration, aging
• Planning: emergency response, housing, transportation

Censuses are expensive and imperfect. Undercounts affect marginalized groups most. Still, no other tool provides a complete snapshot of a whole population at a single point in time.