This report presents 1980 census information on the population size and geographic distribution of more than 100 ancestry groups in the United States. The general ancestry question was based on self-identification, provided no prelisted categories, and allowed for one or more ancestry responses. This was the first census to collect ethnic data on persons regardless of the number of generations removed from their country of origin. Ethnic information collected in previous censuses came from questions on country of birth of persons and their parents and identified ethnicity for only foreign-born or native persons of foreign of mixed parentage.