Enumerators of the 1870 census were instructed to record the names of every person in the household. Added to this, enumerators were presented with printed instructions, which account for the greater degree of accuracy compared with earlier censuses. Enumerators were asked to include the following categories in the census: name; age at last birthday (if a child was under one year of age, months of age were to be stated as fractions, such as 1/12); sex; color; profession; occupation or trade of every male and female; value of real estate; place of birth; whether mother and father were of foreign birth; whether born or married within the year and the month; those who could not read; those who could not write; whether deaf, dumb, blind, or insane or "idiotic". No relationships were shown between members of a household. The categories allowed Congress to determine persons residing in the United States for collection of taxes and the appropriation of seats in the House of Representatives.
The United States was the first country to call for a regularly held census. The Constitution required that a census of all "Persons...excluding Indians not taxed" be performed to determine the collection of taxes and the appropriation of seats in the House of Representatives. The first nine censuses from 1790-1870 were organized under the United States Federal Court system. Each district was assigned a U.S. marshal who hired other marshals to administer the census. Governors were responsible for enumeration in territories.
The official enumeration day of the 1870 census was 1 June 1870. All questions asked were supposed to refer to that date. The 1870 census form called for the dwelling houses to be numbered in the order of visitation; families numbered in order of visitation; and the name of every person whose place of abode on the first day of June 1870 was with the family.
Taken from Chapter 5: Research in Census Records, The Source: A Guidebook of American Genealogy by Loretto Dennis Szucs; edited by Loretto Dennis Szucs and Sandra Hargreaves Luebking (Salt Lake City, UT: Ancestry Incorporated, 1997).
In addition to the databases listed at left, FamilySearch is in the process of indexing the 1870 census and has posted date for Arizona, Arkansas, California, Colorado, Dakota Territory, Idaho, Maine, Montana, Nevada, New Mexico, Oregon and Utah. The data is searchable at their pilot website.