The three major race categories distinguished in this report are white, Negro, and other races. Among persons of other races are American Indians, Japanese, Chinese, Filipinos, Koreans, Asian Indians, and Malayans. Negroes and persons of other races taken together constitute nonwhite persons. Persons of Mexican birth or descent who are not definitely Indian or other nonwhite race are classified as white. In addition to persons of Negro and of mixed Negro and white descent, the category Negro includes persons of mixed Indian and Negro descent unless the Indian ancestry very definitely predominates or unless the person is regarded as an Indian in the community.

In order to obtain data on Spanish- and Mexican/Americans for areas of the United States where most of them live, white persons (and white heads of households) of Spanish surname were distinguished separately in five Southwestern States (Arizona, California, Colorado, New Mexico, and Texas). In all other States, Puerto Rican persons (and heads of households) were identified. Puerto Rican comprise persons born in Puerto Rico and persons of native parentage with at least one parent born in Puerto Rico.