Total U.S. Population Count: 3,929,214 (3,231,533 free; 697.681 enslaved)
(Both Secretary of State Thomas Jefferson and President George Washington were certain that there had been an undercount. )
As set out in the Constitution, the Congress wrote the law directing that the census be taken, appointing officers to take the census, and specifying what information was to be gathered. (Public Acts of the First Congress, Second Session, Chapter Two.)
No microdata from the 1800 census of population are available. Aggregate data for small areas, together with compatible cartographic boundary files, can be downloaded from the National Historical Geographic Information System.
In 1790, the Census was taken of the existing states (Delaware, Pennsylvania, New Jersey, Georgia, Connecticut, Massachusetts, Maryland, South Carolina, New Hampshire, Virginia, New York, North Carolina, and Rhode Island), the three districts (Kentucky, Maine, and Vermont) and the Southwest Territory (Tennessee.)
The census schedules (the actual written records of information from each household) were, by legal mandate, posted in "two of the most public places within [each jurisdiction] there to remain for the inspection of all concerned..." Massachusetts developed a printed form for census takers, all other areas simply used lined paper and each census taker created his own schedule format.
A complete set of the schedules, along with summary data for the counties, and, in some areas, for the towns, was filed with the State Department. In 1812, when the British burned the Capitol during the war, the schedules from many of the states were destroyed. Copies had also been filed with District Courts, but many of those had been lost over the years. The records are not complete.
Remaining records are in the United States National Archives. To view microfilm of released census schedules (all schedules more than 72 years old) contact the regional NARA center at Laguna Niguel. Digitized versions can be accessed through Ancestry.com.
Further information on the first census can be found in Heads of Families at the First Census 1790: Records of the State Enumerations: 1782-1785.