By tracing a single family through several censuses, it's possible for a genealogist to piece together an incredible amount of information, not only about family relationships but about how ancestors lived, their movements, their educations and their professions. Locating as many census records as possible pertinent to a particular family enables a genealogist to detect and eliminate any errors in the original records.
The 1790 census identified only heads of households by name, then enumerated the people in each household in five categories: white males over 16, white males under 16, white females, other free persons and slaves. While succeeding censuses sought additional information, those conducted through 1840 continued to summarize the data for each household, identifying only the head by name. Nonetheless, it's possible, by comparing successive census entries and relating them to any facts turned up in other records, to determine the approximate ages and death dates of individuals within the family.
In 1850, the Census Bureau made a major innovation of great significance to genealogists. For the first time, the census identified every individual by name, age, sex and color. Birthplaces of children, also recorded for the first time in 1850, are clues to earlier residences of migrant families.
In 1860, the census included American Indians for the first time. Information on the value of individual property holdings, added in 1870, provides a clue to the existence of wills and deeds in county courthouses.
In 1880, the Census Bureau made still more additions of particular genealogical significance. Census information included the relationship of each person to the head of the family, the marital status of each person and the place of birth of his or her mother and father. While relationships weren't described in earlier censuses, they can often be inferred, but assumptions should be confirmed through other sources before being accepted as facts.
Information in the 1900 census included months and years of birth, the lengths of marriages and the number of children of each adult woman. If immigrant ancestors were alive at the time of the 1900 census, a genealogist can learn the year of their immigration, a fact which may lead to ship passenger lists and other documents that will help carry a search abroad. Researchers may obtain a one-page summary of the information covered in each census from 1790 to 1970 from the U.S. Department of Commerce, Bureau of the Census, Pittsburg, KS 66762.
Genealogists can try to locate census records any time they've pieced together sufficient data on an ancestral family during a census year, but it's most likely that they'll find their ancestors in the later 1880 or 1900 censuses and then, with additional clues, trace them back into earlier ones. Because the 1880 and 1900 censuses collected so much detailed information, locating ancestors in them can be like opening a genealogical goldmine.
By searching the census records in person at an institution that has microfilm copies, a genealogist can investigate a variety of surnames, check for variations in spelling and compare the information in one census to that in another. In order to get the greatest use out of census records, a researcher needs to be absolutely scrupulous in researching them. Every bit of information contained in the records, as well as some details that don't seem relevant at first may prove useful later, should be copied down. As in all genealogical research, one fact often leads to another.