Eva Castillo came to the United States from Venezuela in the 1970s and quickly took on a leadership role in her community.

But despite her activism she went for decades without fully understanding the importance — to immigrants especially — of a fundamental but low-profile duty of government: the U.S. census.

Now director of the New Hampshire Alliance for Immigrants and Refugees, Castillo recognizes that most Americans pay little attention to the census. But in immigrant communities, participation is hindered by added fear and resistance to government employees collecting sensitive information.

“Immigrants don’t really understand the purpose of the census, to tell you the truth … how it would be to their benefit and how it might hurt them if they don’t answer,” Castillo said. “The governments (where they come from) are usually corrupt and bad and mean, so why would I step outside of my comfort zone and give them all of my data. It is a scary thing — it’s fear of authority and fear of government. And especially in this government — forget it.”

For advocates and public officials, a complete count is necessary to maximize the effective delivery of government resources. The census data are used in a variety of vital ways, from helping to determine the allocation of federal tax dollars to the shape and distribution of congressional districts.

But research by the U.S. Census Bureau shows that some communities, particularly minority and immigrant groups, are far less likely to be accurately counted.

An analysis by the University of California Berkeley estimated that about 18 percent of New Hampshire’s population falls into one of several “hard to count” categories, including minorities, non-native English speakers and low-income households.

For some populations, the problems come down to logistics — it’s harder to gather census data from everyone who lives in a large apartment complex than it is on a street of single-family homes. Other groups face different pressures.

For some immigrants, U.S. census forms recall registration requirements imposed by authoritarian regimes in their native countries — not to mention the “special registration” that the U.S. government imposed on some immigrants after 9/11.

“After 9/11, we lost about a third of our community. People were being harassed and detained. People were hired to spy on us. A lot of people just picked up and left and went to Canada or Europe,” said Kashif Hussain, a 41-year-old Pakistani-born engineer who runs the Pakistani American Youth Society in Brooklyn, N.Y.

The neighborhood only now has recovered most of its immigrant Muslim population, Hussain said. But people still have a hard time believing the United States wants to count them to help distribute funds that would help them.

“People look around and say, ‘Where is this money?’ That’s how they think,” said Hussain. “People just hear the hateful rhetoric from the government and think nothing good is going to come out of it in the Trump era, and they look at everything that happens with a lot of suspicion.”

When the U.S. Census Bureau held focus groups in Michigan composed of Arabic speakers, it found that immigrants were wary of answering questions from the government, even from census workers, and assumed their answers would be shared with other government agencies. Even recruiting Arabic speakers for the focus groups was more difficult than it was for other groups, a 2018 Census Bureau report said.

About 4.6 million U.S. residents have roots in majority-Muslim countries, though many are not Muslims. Three-quarters are U.S. citizens, and 41 percent are American-born.

There are more than 1.2 million Arabic speakers in the United States, two-thirds of them immigrants.

Of particular concern to immigrant advocacy groups for the 2020 census is a proposal from the Department of Commerce that a question about respondents’ citizenship status be added to the survey. The plan has been challenged, and the Supreme Court will soon hear arguments in the case.

Like the Arabic speakers who participated in the Michigan focus groups, people are nervous in the Midwood section of Brooklyn’s Urdu-speaking Pakistani community. There also is fear among recent arrivals from Uzbekistan, who speak the Uzbek language.

“Our clients see the news. They hear the term ‘Muslim ban’ and they know that Trump is President and the administration wants them out of here,” said Ryan Campbell, a staff attorney who counsels immigrants at Midwood’s Council of Peoples Organization.

The Trump administration’s travel ban on some Muslim-majority countries doesn’t include Pakistan. Nevertheless, many Pakistanis in Midwood view it as a sign of government hostility toward Muslims. It has been particularly hard on immigrants who still have close family ties to the old country, Campbell said.

There are similar sentiments among communities of immigrants from Central and South America, given the current administration’s rhetoric.

“People in the immigrant community are terrified of having someone from the government knock on their door and ask personal questions. Because even if they have a green card, even if they’re completely and totally legal, they’re thinking ‘Something could happen to me,’ ” said Jeff Thielman, president and CEO of the International Institute of New England, which assists immigrants and refugees.

Thielman said it benefits everyone — legal immigrant, illegal immigrant and native-born American — to have an accurate count of the people in each district, so he encourages everyone to participate in the census regardless of their status, but he understands that’s easier said than done.

“It’s easy for me to say ‘Go ahead and answer that question,’ but I would say, ‘Yes, just be counted,’ ” Thielman said.

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Union Leader reporter Todd Feathers and Stateline contributed to his report.