The history of the U.S. census since 1790

The United States has counted its population every 10 years since 1790. The U.S. Constitution requires this decennial census to apportion the number of seats each state has in the U.S. House of Representatives, according to the U.S. Census Bureau. Over time, the census added new questions and adopted new methods to keep pace with a growing nation, the bureau says.

From the first count to printed schedules, 1790–1840

Article 1, Section 2 mandates a population count every 10 years to apportion representation, according to the U.S. Census Bureau. On March 1, 1790, President George Washington signed the 1790 Census Act into law, assigning U.S. marshals to conduct the count, the bureau says. As of Aug. 2, 1790, marshals gathered the name of each head of household and tallied residents by age, sex, status (free or enslaved), and other categories then used, reporting a total of 3,929,214 people, according to the bureau.

Early censuses used hand-drawn forms and varied by locality. In 1830, Congress authorized uniform printed schedules to standardize the information collected, according to the Census Bureau. The set of questions expanded in these decades, adding manufacturing data in 1810, agricultural data in 1820, and questions on schools and school attendance in 1840, the bureau says.

Naming every person and professionalizing the count, 1850–1890

Beginning in 1850, marshals listed the name of every free person along with demographic details such as occupation, place of birth, and marital status, according to the Census Bureau. The Census Act of 1880 replaced U.S. marshals and their assistants with specially hired and trained enumerators, the bureau says. The 1880 census collected so much data that it took a decade to tabulate and publish.

To speed processing in 1890, the Census Bureau used mechanical tabulators designed by former Census employee Herman Hollerith, according to the bureau. Enumerators used a separate schedule for each family and gathered more detailed information on family, employment, health, education, and home ownership than before, the bureau says. One hundred years after the first census, the 1890 tally reported nearly 63 million residents, according to the bureau.

A permanent Census Bureau and evolving oversight, 1902–1930s

Recognizing the need for a continuous, specialized workforce to collect demographic, economic, agriculture, and governments data, Congress made the U.S. Census Bureau a permanent agency in 1902, according to the Census Bureau. The bureau notes that oversight shifted across departments: the Secretary of State oversaw censuses through 1850; the Department of the Interior supervised 1850 to 1900; a permanent Census Bureau was created in 1902; it moved to the Department of Commerce and Labor following that department’s establishment on Feb. 14, 1903; and it has been part of the Department of Commerce since the departments split into separate agencies on March 4, 1913.

Questionnaires also evolved. Following the 1929 Stock Market Crash and start of the Great Depression, the 1930 census included a standard questionnaire on topics such as demographic, citizenship, occupation, employment, and veterans status, and a supplemental questionnaire to help the government better understand the crisis’s impact on workers, according to the Census Bureau. The bureau later introduced statistical sampling to collect additional detail without unduly increasing the overall burden on respondents and data processing.

Sampling, computing, and streamlined forms, 1940–1970

The 1940 census was the first to use statistical sampling, which selects a portion of the population to answer additional questions so results can represent the whole, according to the Census Bureau. This approach allowed expanded demographic detail while reducing processing burdens, the bureau says. In processing, UNIVAC I replaced mechanical tabulators in the 1950s, and the 1960 census replaced punch cards with the Film Optical Sensing Device for Input to Computers (FOSDIC), according to the bureau.

Sample questions changed by decade, including means of transportation to work in 1960 and occupation five years ago in 1970, the Census Bureau says. In 1970, the bureau conducted the first true test of a “mail-out, mail-back” census and asked respondents to self-identify their race, according to the bureau. California was the most populous state in 1970, and Hispanic origin was included as a separate question, the bureau says.

Expanding mail response and digital access, 1980–2000

The success of the 1970 mail questionnaire led to an expansion in 1980, when about 95% of the U.S. population was counted by mail, according to the Census Bureau. In 1990, computerized mapping systems debuted, CD-ROMs of census returns were introduced, and for the first time anyone with a personal computer could access some census data online, the bureau says. The 2000 census allowed some who received the short-form questionnaire to respond via the internet for the first time and used a paid advertising campaign that reached 99% of U.S. residents in 17 languages, according to the bureau.

From long-form samples to the American Community Survey, 2005–2010

In 2005, the annual American Community Survey replaced sample questions on the decennial census questionnaires, according to the Census Bureau. As a result, the 2010 census used a single short form with 10 questions for the population it counted, the bureau says. The bureau notes that due to cybersecurity concerns, respondents could not submit answers over the internet in 2010 and that same-sex married couples were counted.

The digital era of address updates and online response, 2020

Ahead of 2020, the Census Bureau used satellite imagery to update the Master Address File, reviewing 100% of addresses and validating 65% in-office to reduce in-field canvassing, according to the bureau. The 2020 census was the first in which all households had the opportunity to respond online, with responses also accepted by mail, by phone, through enumerators, or administrative records; enumerators used mobile devices to securely collect and transmit data, the bureau says. The bureau also cites the use of satellite imagery to update its address file and electronic devices allowing instant data upload in the field.

Public access to historical records

Census records are confidential for 72 years. The National Archives released 1940 census records in April 2012 and 1950 census records in April 2022, according to the U.S. Census Bureau. The bureau notes that many 1790–1810 records were destroyed during the War of 1812 and most 1890 records were destroyed in a 1921 fire, with some substitute records available.