In August 1939, Congress authorized the director of the census to conduct a national census of housing "in each state, the District of Columbia, Hawaii, Puerto Rico, the Virgin Islands, and Alaska, in the year 1940 in conjunction with, and at the same time, and as part of the population inquiry of the sixteenth decennial census." The census was "to provide information concerning the number, characteristics (including utilities and equipment), and geographic distribution of dwelling structures and dwelling units in the United States."
Because the originating legislation came so late in the census planning process and because the nature of the questions was so different from those in the census of population, the housing inquiries in the 1940 census were collected via a separate census. In practice, enumerators collected information for the housing census at the same time they collected information for the population census.
One of the major innovations of the 1940 census was the use of advanced statistical techniques, including probability sampling, which had been used only on an experimental basis before. Sampling had been tested in a trial census of unemployment carried out by the Civil Works Administration in 1933-1934 and surveys of retail stores in the same decade, and an official sample survey of unemployment in 1937 that covered about 20,000 households.
Sampling in the 1940 census allowed the addition of a number of demographic questions of enumerated persons without unduly increasing the overall burden on respondents and on data processing. It also made it possible to publish preliminary returns 8 months ahead of the complete tabulations. Sampling also allowed the Census Bureau to increase the number of detailed tables published and review the quality of the data processing with more efficiency.
Several new questions reflected the concerns of the depression years. Along with the new census focusing on the condition of the nation's housing stock and the need for public housing programs, the 1940 census included questions about employment, unemployment, internal migration and income.