The total population was determined to be 9,638,453, of which 1,538,022 were slaves. The center of population was about 120 miles (193 km) west-northwest of Washington in Hardy County, Virginia (now in West Virginia).
This was the first census in which any states recorded a population of over one million—New York, Virginia, and Pennsylvania—as well as the first in which a city recorded a population of over 100,000—New York. It was also the first census in which Baltimore was ranked as the country's second-most populous city. Thirdly, in this census and the 14 subsequent ones, New York was the most populous state until being superseded by California in the 1970 census.
The 1820 census contains a great deal more information than previous censuses. Enumerators listed the following data in columns, left to right:
Name of the head of family
of free white males under age 10
of free white males age 10 to under 16
of free white males age 16 to 18
of free white males age 16 to under 26
of free white males age 26 to under 45
of free white males age 45 and up
of free white females under age 10
of free white females age 10 to under 16
of free white females age 16 to under 26
of free white females age 26 to under 45
of free white females age 45 and up
of foreigners not naturalized
of persons engaged in agriculture
of persons engaged in commerce
of persons engaged in manufacture
of male slaves under 14
of male slaves age 14 to under 26
of male slaves age 26 to under 45
of male slaves age 45 and up
of female slaves under 14
of female slaves age 14 to under 26
of female slaves age 26 to under 45
of female slaves age 45 and up
of free male colored persons under 14
of free male colored persons age 14 to under 26
of free male colored persons age 26 to under 45
of free male colored persons age 45 and up
of free female colored persons under 14
of free female colored persons age 14 to under 26
of free female colored persons age 26 to under 45
of free female colored persons age 45 and up
of all other persons except Indians not taxed
Several of these columns were for special counts, and not to be included in the aggregate total. Doing so would have resulted in counting some individuals twice. Census takers were asked to use double lines, red ink or some other method of distinguishing these columns so that double counting would not occur. For example, the count of free white males between 16 and 18 was a special count, because these individuals were also supposed to be tabulated in the column for free white males of age 16 and under 26.
The other special counts were foreigners not naturalized, persons engaged in agriculture, persons engaged in commerce, and persons engaged in manufacture.
Census takers were also instructed to count each individual in only one of the occupational columns. For example, if an individual was engaged in agriculture, commerce, and manufacture, the census taker had to judge which one the individual was primarily engaged in.
Censustaking was not yet an exact science. Before 1830, enumerators lacked pre-printed forms, and drew up their own, sometimes resulting in pages without headings, line tallies, or column totals. As a result, census records for many towns before 1830 are idiosyncratic. This is not to suggest that they are less reliable than subsequent censuses, but that they may require more work on the part of the researcher.
^Between 1790 and 1860, the state of West Virginia was part of Virginia; the data presented here reflects the present-day boundary and is also included in the total population of Virginia.
^The District of Columbia is not a state but was created with the passage of the Residence Act of 1790. The territory that formed that federal capital was originally donated by both Maryland and Virginia; however, the Virginia portion was returned by Congress in 1846.
^The relevant note on p. 10 erroneously switches the population values for Perry and Washington counties. The correct values can be found on page 121 of the final census report for 1820.