The available data differ somewhat from decade to decade, according to what was collected in the census and the items chosen for transcription to electronic form. For the early decades, most of the enumerated items are included. For later decades, only a portion of characteristics have been transcribed. No information is available below the county level, and only states are included (no information on western territories before statehood, or for the District of Columbia).
In addition to basic counts of population and housing units, all decades contain information on race, gender, and some measure of household size and composition. Beginning with 1840, some economic characteristics such as education and occupation are included. Later decades have many variables, including ancestry, literacy, and income variables. In a few cases, the census data were augmented with information from the U.S. Department of Agriculture and the National Council of Churches of Christ.