In 1880, the U.S. Census Bureau began asking a question in the decennial census of population to determine how each person living in a household was related to the head of the household (or the householder, in current terminology). From this information, all individuals can be tabulated according to their relationship to the householder, such as spouse, child, etc., and households may be classified as belonging to a particular type, such as married-couple, nonfamily, etc. This report uses the latter approach, classifying households, and shows tabulations of households within specific individual relationships and certain broader household-type classifications. 

Beginning in the 1990 census, relationship data included separate precoded classifications for unmarried partner, stepchild, and grandchild. Census 2000 added more precoded categories (foster child, adopted child, parent-in-law, child-in- law) and obtained more detailed information about relationship than did previous censuses. 

The new information collected in the relationship-to-householder item reflects the growing complexity of American households and creates an opportunity to enhance our understanding of how the U.S. population collectively lives in households. Since the general classifications used to group household types changed minimally over the last half of the 20th century, the traditional aggregations may not fully reflect this increased complexity.