One common place to get information about U.S.-resident families is from federal census records. The federal census has been taken every ten years since 1790 and shows who was living in a particular household in the given census year. Between 1790-1840, only the head of household’s name was provided; all other family members' names were not listed, but their age categories were provided (for example, the number of individuals age 0-10, 10-16, etc.). Generally, these census records do not record the names of slaves, making census searches far less useful for African-Americans.
From the 1850 census on, each household member’s name was listed in the census data. With each census taken, more inquiries were placed on the census form in the hopes of obtaining more detailed information about each family. Because of the tremendous volume of information, a census index can save many hours of fruitless, frustrating research. The index lists the exact page number(s) that your family is listed on so that you can more easily access the information you want on the census microfilm reel. The type and completeness of each index varies. For 1860 and 1870, most censuses are indexed only by individual county within a state. The 1880 and 1900-1920 census is indexed using the "soundex" system, but lists only heads of household with children under 10. More recent censuses are more fully indexed. Unfortunately, most of the 1890 census was destroyed by fire, but a small amount of it still remains. This library has microfilm records of that surviving information.
Due to a 72-year privacy law, the most recent census that can be accessed today is the 1940 census. The 1940 census records were made available April 1, 2012. Many libraries, state and local historical societies, and state archive offices have microfilm copies of at least local census records.
There are a number of cautions that the user must observe. Census-takers can get the name wrong, fail to survey each address or survey the same family more than once, or record other information incorrectly. They especially had difficulty in accurately recording information from immigrants whose English was imperfect. Microfilmers can also have made mistakes in processing the records. In certain cases, undercounts were deliberately done, while in others, records were padded to increase population counts.