The United States Census of 1800 was the second Census conducted in the United States. It was conducted on August 4, 1800.
It showed that 5,308,483 people were living in the United States, of whom 893,602 were slaves. The 1800 Census included the new District of Columbia. The census for the following states were lost: Georgia, Kentucky, New Jersey, Tennessee, and Virginia.
The 1800 census asks the following information in columns, left to right: 
|1||Name of the head|
|2||Number of free white males under age 10|
|3||Number of free white males of age 10 and under 16|
|4||Number of free white males of age 16 and under 26|
|5||Number of free white males of age 26 and under 45|
|6||Number of free white males of age 45 and over.|
|7||Number of free white females under age 10|
|8||Number of free white females of age 10 and under 16|
|9||Number of free white females of age 16 and under 26|
|10||Number of free white females of age 26 and under 45|
|11||Number of free white females of age 45 and over.|
|12||Number of all other free persons|
|13||Number of slaves|
This census is one of the several for which some of the original data are no longer available. Original census returns for Georgia, Kentucky, Mississippi, New Jersey, Tennessee, and Virginia were lost over the years. 
No microdata from the 1800 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.
|District||Free white males under age 10,||Free white males age 10–16||Free white males age 16–26||Free white males age 26–45||Free white males over age 45||Free white females under age 10||Free white females age 10–16||Free white females age 16–26||Free white females age 26–45||Free white females over age 45||All other free persons||Slaves||Total|
|New York (excluding Duchess, Ulster, Orange counties)||83,161||36,953||40,045||52,454||25,497||79,154||32,822||39,086||47,710||23,161||8,573||15,602||484,065|
|New York ( Duchess, Ulster, Orange counties)||16,936||7,320||9,230||9,140||6,358||16,319||6,649||9,030||8,701||5,490||1,801||5,011||101,985|
|Pennsylvania (eastern district)||52,767||24,438||29,393||33,864||20,824||51,176||23,427||29,879||30,892||19,329||11,253||557||327,979|
|Pennsylvania (western district)||50,459||21,623||24,869||25,469||17,761||48,448||20,362||24,095||22,954||14,066||3,311||1,149||274,566|
|Maryland (including Washington County in the District of Columbia a[›], but excluding parts of Baltimore County)||33,520||16,581||20,560||22,169||12,617||32,463||15,718||21,506||20,363||11,240||18,646||102,465||317,348|
|Maryland (additional return for Baltimore County)||567||226||318||343||249||517||222||375||318||199||41||847||4,276|
|Virginia (eastern district)||57,837||25,998||32,444||34,588||19,087||54,597||25,469||34,807||32,641||18,821||13,194||322,199||676,682|
|Virginia (western district)||34,601||14,502||16,264||15,674||11,134||32,726||13,366||15,923||3,632||15,169||1,930||23,597||203,518|
|Virginia ( Alexandria and part of Fairfax County in the District of Columbia a[›])||889||320||483||557||221||670||313||479||473||189||383||1,172||5,949|
|Indiana Territory||854||347||466||645||262||791||280||424||393||115||163||135||5,641 b[›]|
|District||Free white males under age 10||Free white males age 10–16||Free white males age 16–26||Free white males age 26–45||Free white males over age 45||Free white females under age 10||Free white females age 10–16||Free white females age 16–26||Free white females age 26–45||Free white females over age 45||All other free persons||Slaves||Total|
|Maryland corrected d[›]||36,751||17,743||21,929||23,553||13,712||34,703||16,787||22,915||21,725||12,180||19,987||107,707||349,692|
^ a: At the time of the 1800 Census, the territory donated to form the District of Columbia was still being administered by the states of Maryland and Virginia. The state of Maryland included the population of the District under its control within its own return. The population of the District of Columbia within Maryland was 8,144 persons, including 5,672 whites, 400 free blacks, and 2,472 enslaved persons.
^ b: Persons 766 added to the particular items of this return.
^ c: This return has been received since the communication of the above Aggregate to Congress.
- "1800 Census Questions". Archived from the original on April 27, 2010. Retrieved May 3, 2010.
- Dollarhide, William (2001). The Census Book: A Genealogists Guide to Federal Census Facts, Schedules and Indexes. North Salt Lake, Utah: HeritageQuest. p. 8.
- "District of Columbia – Race and Hispanic Origin: 1800 to 1990" (PDF). U.S. Census Bureau. September 13, 2002. Archived from the original (PDF) on August 4, 2011. Retrieved November 1, 2011.
- "Enumeration of Persons in the several districts of The United States" (PDF). 1800. p. 3. Archived from the original (PDF) on June 11, 2010. Retrieved May 10, 2010.
- Population of the 100 Largest Cities and Other Urban Places in the United States: 1790 to 1990, U.S. Census Bureau, 1998
- "Regions and Divisions". U.S. Census Bureau. Archived from the original on December 3, 2016. Retrieved September 9, 2016.