[3] In 2020, every household received an invitation to complete the census over the Internet, by phone or by paper questionnaire.

Title 13 of the United States Code governs how the census is conducted and how its data are handled.

Decennial U.S. census figures are based on actual counts of persons dwelling in U.S. residential structures.

Usual residence, a principle established by the Census Act of 1790, is defined as the place a person lives and sleeps most of the time.

[6] In instances where the bureau is unsure of the number of residents at an address after a field visit, its population characteristics are inferred from its nearest similar neighbor (hot-deck imputation).

Certain American citizens living overseas are specifically excluded from being counted in the census even though they may vote.

"Private U.S. citizens living abroad who are not affiliated with the federal government (either as employees or their dependents) will not be included in the overseas counts.

In 2020, the earliest responses were collected starting January 21 in remote parts of Alaska, and March 12 for most Americans.

[11] In the 1850s, census planners suppressed information about slavery due to pressure from Southern lawmakers.

[11] The results of the 1920 census were ignored and no reapportionment took place, as rural lawmakers feared losing power to urban areas.

Democrats often argue that modern sampling techniques should be used so that more accurate and complete data can be inferred.

[19] Following the decision, Trump issued an executive order directing the department to obtain citizenship data from other federal agencies rather than via the census.

[20] On July 21, 2020, Trump signed a presidential memorandum ordering the exclusion of illegal immigrants from the numbers in the 2020 census that are used to apportion seats in the House of Representatives.

On August 3, the department announced its Replan Schedule that would end collection early on September 30, aware this would leave them with incomplete data that they would have to estimate total numbers to complete.

[22] Around the same time, Trump issued a memo to the Commerce Department on July 21, 2020, instructing them to use estimates of undocumented immigrants and subtract their numbers from the totals, claiming that he had the authority to make this determination on a Constitutional and past legal basis.

[12] Several legal challenges were filed, and a combined suit from 22 states and several non-governmental organizations were found against Trump, ruling that only Congress has the authority to interpret the manner of which people the census includes.

[25] Between 1781 and 1786, the first "actual enumeration" was conducted separately in each state and compiled by John Kean for consideration at the Constitutional Convention in 1787.

The censuses also spread geographically, to new states and territories added to the Union, as well as to other areas under U.S. sovereignty or jurisdiction.

Censuses of the late 19th century also included agricultural and industrial schedules to gauge the productivity of the nation's economy.

[31] The total population, of 62,947,714, was announced after only six weeks of processing (punched cards were not used for this family, or rough, count).

[36] One explanation for this number is that it was chosen in 1952[37] as slightly higher than the average female life expectancy, 71.6.

Under the administration of President Franklin D. Roosevelt, the Federal Bureau of Investigation (FBI), using primarily census records, compiled (1939–1941) the Custodial Detention Index ("CDI") on citizens, enemy aliens, and foreign nationals, who might be dangerous.

The Second War Powers Act of 1941 repealed the legal protection of confidential census data, which was not restored until 1947.