Every ten years, the U.S. Census Bureau gathers basic information about people and households for the entire American population, such as age, gender, race and number of people in a home. For the first time since 1950, the census will again ask about citizenship.

Last night, the Department of Commerce, which oversees the U.S. Census Bureau, decided to add a question that will ask whether or not you are a citizen. Commerce Secretary Wilbur Ross outlined the justification for adding the question in a memo. This question would give nationwide detail on citizenship down to the block level. The Department of Justice requested the new question, saying that it would help enforce the Voting Rights Act, which protects minority voting rights. Next, the Census Bureau must submit the final list of 2020 census questions to Congress by the end of the month.

However, many experts, advocates and politicians are concerned that the addition of the citizenship question, especially under an anti-immigrant administration, could discourage people from filling out the survey. The California Attorney General Xavier Becerra, who was also part of a coalition of attorneys general who urged against the question, will file a lawsuit against the Trump administration, arguing that "Including the question is not just a bad idea — it is illegal." 

This potential for an undercount could undermine the accuracy of the data, and have far-reaching impacts on representation, services and research. Data from the census are used to determine how electoral districts are drawn, over $600 billion in federal funding are distributed and much more.

Using the most recent five-year American Community Survey (ACS), which is based on a large sample of the population, Social Explorer visualized the areas of the country that would be most affected by the addition of the question. According to the 2012-16 ACS, there were 22,214,947 non-citizens in the U.S., representing 7.0 percent of the nation's population. The following map shows where non-citizens live at the county level. Click around the map to explore. 

As you explore the map, you may also select different geography levels from state to census tract, as well as school district and election district boundaries. The following map shows the non-citizen population by congressional district.

The areas with the most non-citizens are also the places that could see the biggest changes in representation if redistricting policy is challenged. Social Explorer's Andrew Beveridge has commented extensively on the issue, including in this article. 

For more on how future court cases could change redistricting by counting eligible voters instead of all residents, check out Social Explorer's Webby Award-winning project "The Threat to Representation for Children and Non-Citizens" that shows the impact that Evenwel v. Abbott  the 2015 Supreme Court case could have had.