Just how many people live in Philly, the U.S.? Here’s why that’s a tough question to answer.

The U.S. government has been trying to count its citizens completely and accurately every 10 years since 1790, but in 2020 it will encounter some fresh obstacles.

They include digital divides as the Census Bureau encourages online responses for the first time, and a growing trend of government mistrust deepened in immigrant communities by the possibility of a citizenship question on the questionnaire.

Those hurdles could worsen miscounts in communities that are traditionally undercounted.

So Philadelphia is doing things differently this time around.

For the 2010 Census, it started planning six months before the count began. For the 2020 Census, the planning began in January, or 15 months before the count is to start. And efforts here, statewide, and nationwide are focused on reducing the undercounting.

At stake are seats in the U.S. House, the boundaries of voting districts, and hundreds of billions in federal funds allocated to states.

“An undercount anywhere affects Philadelphia,” said Stephanie Reid, executive director of Philly Counts 2020, a city effort to support the census. “Philadelphia wins when the whole state wins.”

Children under 5 are the fastest growing group that is undercounted, said Jeff Behler, director of the Census Bureau’s New York Regional Office, which covers New Jersey. Sometimes their parents don’t think to count them. Sometimes they think they are protecting their children’s privacy. Sometimes children are staying with grandparents or several caretakers who don’t count them.

Residents in low-income communities with fewer resources and in rural communities are more likely not to have internet access.

People who rent rather than own their homes, who do not speak English, who are homeless, or who move around a lot are more difficult for the Census Bureau to reach. Immigrants and people of color may mistrust the government.

"If [residents] don’t get counted now in 2020, if they choose not to participate or get others in their community not to participate because of fear, that’s gonna affect their community for the next 10 years,” Behler said.

Based on demographics and previous response rates, the Census Bureau has determined locations where it expects low response rates and where it needs to focus resources.

Some people don’t fill out the forms because they don’t see the point of the census, or they’re busy.

Representatives from the Census Bureau, municipalities, and community groups agree that fewer people trust the government now than they did during previous census counts. That makes persuading people to give personal information to the government more difficult.

On top of that, for the first time, the bureau is encouraging people to enter their information online, which raises questions about cybersecurity for some and is a barrier for others without internet access. Philadelphia was the only large city in which internet access dropped from 2016 to 2017.

The U.S. Supreme Court is expected to decide next month whether to allow the Trump administration to add a question to the 2020 Census asking for residents’ citizenship status. The Census Bureau has said the question will deter millions of people, particularly noncitizens, from submitting their forms.

Among the places the Census Bureau anticipates low mail-in response rates in 2020 are North Philadelphia; West Philadelphia; Camden; the City of Chester; West Chester Borough; the City of Coatesville, Chester County; Atlantic City; Trenton; and Lindenwold Borough, Camden County.

The Census Bureau uses its mapping tool to see which neighborhoods are less likely to fill out census forms and to figure out where to place workers and encourage communities to form census committees.

The bureau is working with community groups and libraries to host job fairs to hire people from hard-to-count communities who know their neighborhoods, know the challenges they face, and can better persuade neighbors to answer census forms.

Two of the bureau’s buzzwords are “trusted voices.” The bureau is preaching the importance of the census to religious leaders, store owners, Native American tribe leaders, mayors of small towns, neighborhood activists, and anyone else who might be someone whose word community members already believe.

“We’re aware we have to build big trust,” said Fernando Armstrong, director of the Census Bureau’s Philadelphia regional office.

The bureau is trying to convince people of three main points about the 2020 Census: that it is safe, easy, and important. The bureau is barred by law from sharing information it gathers from individual households with anyone, including other federal agencies. It’s emphasizing the general ease of responding online at home or at a community center or library. It’s hammering home the stakes in money and influence.

Keystone Counts, a statewide coalition of nearly 70 nonprofits, is testing 2020 Census messages on focus groups to figure out what might motivate people to complete their forms. Some people are motivated more by political representation or funding or the opportunity to prevent policy makers from marginalizing their communities.

Jo Lin, coalition manager, said some of the communities the nonprofits serve “are invisible to policy makers” because population counts don’t reflect their size. So the groups are eager to do anything they can to ensure people are counted.

Keystone Counts started planning for the census in 2017.