United States Census, 1840

The United States Census of 1840 was the sixth census of the United States. Conducted by the Census Office on June 1, 1840, it determined the resident population of the United States to be 17,069,453 — an increase of 32.7 percent over the 12,866,020 persons enumerated during the 1830 Census. The total population included 2,487,355 slaves. In 1840, the center of population was about 260 miles (418 km) west of Washington, near Weston, Virginia.

The 1840 Census was the first that attempted to count Americans who were "insane" or "idiotic". Published results of the census indicated that alarming numbers of black persons living in non-slaveholding States were mentally ill, in striking contrast to the corresponding figures for slaveholding States.

Pro-slavery advocates trumpeted the results as evidence of the beneficial effects of slavery, and the probable consequences of emancipation. Anti-slavery advocates contended, on the contrary, that the published returns were riddled with errors, as detailed in an 1844 report by Edward Jarvis of Massachusetts in the American Journal of the Medical Sciences, later published separately as a pamphlet, and in a memorial from the American Statistical Association to Congress, praying that measures be taken to correct the errors.

The memorial was submitted to the House of Representatives by John Quincy Adams, who contended that it demonstrated "a multitude of gross and important errors" in the published returns. In response to the House's request for an inquiry, Secretary of State John C. Calhoun reported that a careful examination of the statistics by the supervisor of the census had fully sustained their correctness. The returns were not revised.

The 1840 census asked these questions:

No microdata from the 1840 population census are available, but aggregate data for small areas, together with compatible cartographic boundary files, can be downloaded from the National Historical Geographic Information System. A compendium of data from the sixth census, organized by States, counties, and principal towns is available on the web site of the Census Bureau.

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