The fourth census was taken under the provisions of an act of March 14, 1820. The enumeration began on the first Monday of August, and was scheduled to conclude within 6 calendar months; however, the time prescribed for completing the enumeration was extended to September 1, 1821. The 1820 census act required that enumeration should be by an actual inquiry at every dwelling house, or of the head of every family within each district.
Data relating to manufactures were collected by the assistants, sent to the marshals, and then transmitted to the Secretary of State at the same time as the population returns. The report on manufactures presented the data for manufacturing establishments by counties, but the results were not summarized for each district and an aggregate statement was compiled as a result of incomplete returns