Blacks, like whites, are the only other group continuously identified by the census since 1790. The language used to refer to Blacks has changed over the decades. After slavery ended, during the second half of the 19th century, census data helped drive scientific theories of race that were used at the time to justify discrimination. That's why the census added "quadroons" and "octoroons" as categories in 1890. These were the instructions given that year to enumerators:
Write white, black, mulatto, quadroon, octoroon, Chinese, Japanese, or Indian, according to the color or race of the person enumerated. Be particularly careful to distinguish between blacks, mulattoes, quadroons, and octoroons. The word 'black' should be used to describe those persons who have three-fourths or more black blood; 'mulatto,' those persons who have from three-eighths to five-eighths black blood; 'quadroon,' those persons who have one-fourth black blood; and 'octoroons,' those persons who have one-eighth or any trace of black blood.
"Koreans" also appeared (in 1920-1940), disappeared (1950-1960) and reappeared (in 1970) following trends in immigration.
The "Chinese" were first counted in 1860, but only in California. By the 1870 census, the Chinese constituted the first major wave of non-European immigrants to the U.S. since the end of the slave trade. That year, according to the Census Bureau, "Chinese" became the first national origin category, beyond color and race.
Questions about Hispanic "origin or descent" were first added in 1970. The following decade, the Census started to differentiate between ethnicity ("Hispanic" or "not Hispanic") and race ("black" or "white"), as it still does today. The complete options, as of 2010, reflect a much more diverse country than in 1790. There has been a proliferation of new racial and ethnic identities (now the government counts Chicanos, Puerto Ricans, Cubans, and Guatemalans) through the revision of old ones ("Indians" have become "American Indians").