(Photo by Flickr user Blue Skyz Studios under Creative Commons License)

(Photo by Flickr user Blue Skyz Studios under Creative Commons License)

Issues of race and ethnicity can be complicated in the United States, and nowhere is that more evident than in the U.S. Census.

The census, which counts every resident in the United States every 10 years, has classified black Americans as a separate race since 1820. But the way the census has referred to Africans Americans has changed repeatedly over the decades.

The evolving category names often reflected the current public attitudes of the time. For example, the term “colored” became “black” and then “Negro,” with “African American” added later. The term “mulatto” appeared in every census until 1920. The definition varied over the decades, but generally referred to a person who is black and at least one other race.

Up until 1950, census takers would determine the race of the people they counted. From 1960 on, Americans could choose their own race. By 2000, Americans could include themselves in more than one racial category. Before that, multiracial people were mostly counted in only one racial category.

(Joss Fong/Vox; data from Pew Research Center)

The way other groups of Americans were referred to also changed over the years.

For example, from 1920 until 1940, Indians from Asia were classified as “Hindu”, whether or not they actually were Hindu. And Mexicans were categorized as a separate race in the 1930 census.

A graphic from the Pew Research Center shows a historical timeline of how the US Census referred to different groups of Americans over the years.