Lawmakers are set to question the Justice Department Friday about why it requested the 2020 census to ask about citizenship. The history of using the U.S. census to ask about citizenship has many twists and turns.

MARY LOUISE KELLY, HOST: 

The Justice Department point person on civil rights heads to Capitol Hill tomorrow for what may be a tough hearing. It is about the 2020 census. The department has requested that the census form include a question about U.S. citizenship. The federal government has used the census to ask people about their citizenship before. NPR's Hansi Lo Wang explains the surprising history.

HANSI LO WANG, BYLINE: This is a story with lots of stops and starts, so we'll need a tour guide.

MARGO ANDERSON: My name is Margo Anderson.

WANG: She's a history professor at the University of Wisconsin in Milwaukee.

ANDERSON: Right. And I'm the author of "The American Census: A Social History."

WANG: And she traces the first time all U.S. households were asked about citizenship all the way back to the census of 1820. Was this still done on horseback at that time?

ANDERSON: Oh, certainly (laughter) - or walking.

WANG: That was the country's fourth headcount. And census takers asked...

ANDERSON: Are there any foreigners not naturalized in your household? And if so, how many?

WANG: Anderson says she's not sure why these questions were included.

ANDERSON: I haven't found yet any evidence of the use of that information in terms of policies, which I think is why it simply disappeared.

WANG: By 1840, the government stops asking about foreigners who are not citizens. Fifty years pass before the topic comes up again in 1890. By this point, the federal government had been asking for decades about where people were born and where their parents were born. Anderson explains why.

ANDERSON: Well, we have lots of immigrants in the country right now. How are they doing?

WANG: So for the 1890 census, people born outside the U.S. were asked how long they've been in the country and whether they've become citizens. And census takers kept asking similar questions well into the 20th century. ...