Individual Census Records from 1790 to 1950 are maintained by the National Archives and Records Administration, not the U.S. Census Bureau.

The 1840 census started June 1, 1840 from What day was the census taken each decade? at the United States Census Bureau. See the 1840 Overview at United States Census Bureau.

Census Instructions

The decennial census has always required a large workforce to visit and collect data from households. Between 1790 to 1870, the duty of collecting census data fell upon the U.S. Marshals. A March 3, 1879 act replaced the U.S. Marshals with specially hired and trained census-takers to conduct the 1880 and subsequent censuses.

During the early censuses, U.S. Marshalls received little training or instruction on how to collect census data. In fact, it was not until 1830 that marshals even received printed shedules on which to record households' responses. The marshals often received limited instruction from the census acts passed prior to each census. 

Beginning with the 1880 census, specially hired and trained census-takers replaced the U.S. marshals. Door-to-door census by temporary census-takers was the primary method of conducting the census until the U.S. Census Bureau began mailing questionnaires to households in 1960.

As more and more households received and returned their questionnaires by mail, the role of census-taker changed. Today, the majority of households are counted by mailed questionnaires. Census-takers visit places frequented by transient households (shelters and soup kitchens, campsites, etc.) and households that do not return their mailed questionnaires (during the "Nonresponse Follow-Up" phase of the census). As a result, the "Instructions to Enumerators" provided here include the congressional acts U.S. marshalls reviewed during the early census, specially-published instructions for door-to-door census, and lastly, guides used for the limited number of personal interviews conducted during nonresponse follow-up operations.

Copied from the Census Intructions at the United States Census Bureauthat show 1790 Instructions, but not again until 1850 Instructions through 2010.

Page 19 - Reel 0074 Allen County, Indiana - Population schedules of the sixth census of the United States, 1840 at Internet Archive

Links to Online Census Records

1. ACGSI.org Annotated Census Records, 1830 & 1840, Allen County, Indiana - Heads of Household and Names from Annotations
2. ACGSI.org 1840 Population Schedule, African American
3. Ancestry.comblank 1840 census form
4. FamilySearch.orgWiki 1840 Census Information
5. FamilySearch.orgbrowse 1840 Indiana Census by Township
6. FamilySearch.orgSearch 1840 U.S. Census Index
7. FamilySearch.orgWiki for Indiana Census 1807 - 1940 links organized by year to various online census records.
8. FindMyPast.com Free US Census 1840
9. Use Steve Morse Census Search Tool for any census
10. Internet Archivepage 19 (n41) images
11. Internet Archive- complete Population schedules of the sixth census of the United States, 1840, Indiana [microform] (Volume Reel 0074 - 1840 Indiana Federal Population Census Schedules - Adams, Allen, Blackford, Bartholomew, Benton, and Boone Counties) - United States. Bureau of the Census reel 74.
12. USGenWeb alphabetical Index 2001
13. USGenWeb page 19 transcriptions 2001 by Teresa Sandum
14. USGenWeb page 31 transcriptions 2001 by Teresa Sandum
15. USGenWeb page 43 transcription 2001 by Teresa Sandum
16. USGenWeb Notes from 2005
17. USGenWeb page 19 transcriptions 2005 by Teresa Sandum
18. USGenWeb page 31 transcriptions 2005 by Teresa Sandum
19. USGenWeb page 38 transcriptions 2005 by Teresa Sandum
20. USGenWeb page 45 transcriptions 2005 by Teresa Sandum
21. USGenWeb page 51 transcriptions 2005 by Teresa Sandum

Other Information

November 10, 2023 post by the U.S. Census Bureau on Facebook:

#ICYMI: The 1840 Census was the first count of our nation's veterans. However, women veterans were not counted until 1980.

Read #AmericaCounts to learn how data collection of #veterans has evolved over time to better understand the changing needs of those who serve in America’s armed forces.

1840 Census Was First to Collect Data on Veteran Status and Only Men Were Considered Veterans Through Most of the Nation’s History

#VeteransDay #CensusData

The Secret Hiding on the 1840 U.S. Census by Amie Bowser Tennant published February 23, 2017 on My Kith N Kin blog. Refers to names on the back of the census where the enumerators recorded Revolutionary War and other service pensions by name and age. The lists also named the head-of-household in which the individual was residing. The names are found in census and the book A census of pensioners for revolutionary or military services [electronic resource] : with their names, ages, and places of residence, as returned by the marshals of the several judicial districts, under the act for taking the sixth census by U.S. Census Bureau; United States. Dept. of State published 1841 available on Internet Archive.