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As mandated by the U.S. Constitution Article I, Section 2, the U.S. census gets just one chance, every 10 years, to count every resident in the United States. The 2020 Census marked the 24th time that the country has counted its population; the first was in 1790. Each home received an invitation to respond to a short questionnaire—online, by phone, or by mail. This marked the first time that everyone could respond to the census online.

The data collected by the census determine the number of seats each state has in the U.S. House of Representatives (a process called apportionment) and is also used to adjust or redraw electoral districts based on where populations have increased or decreased. The results also inform decisions about allocating hundreds of billions of dollars in federal funding to communities across the country—for hospitals, fire departments, schools, roads, and other critical programs and services.

The 2020 Census required counting an increasingly diverse and growing population of around 330 million people in more than 140 million housing units. To get an accurate count, the Census Bureau had to build an accurate address list of every housing unit, maximize self-response to the census, and efficiently follow up with those who did not self-respond.

In the years leading up to 2020, we conducted research in four areas that focus on the major cost drivers of the census:

• Using the Internet to increase self-response.
• Using existing government data sources to answer census questions and reduce follow-up workload.
• Automating operations to increase productivity and reduce staff and offices.
• Using existing maps and address to reflect changes rather than walking every block in every neighborhood in the country.

The decennial census is the largest mobilization and operation conducted in the United States and requires years of research, planning, and development of methods and infrastructure to ensure an accurate and complete count.