The Census Bureau, charged with counting every person living in the United States in the coming decennial, may never find whoever is living in a converted garage on the east side of San Jose.

The property owner has replaced the garage door with siding, painted it the same beige as the rest of the house, and added a small window and front door. The makeshift remodeling is well camouflaged, but there’s another tell — the sidewalk out front slopes down to the street where there was clearly once a driveway.

“There are certain cues we’re looking for,” said Nicholas Almeida, San Jose’s chief service officer. The city knows that thousands of people are living in units like this, technically illegal, with no recognized address. Their hidden households have extra satellite dishes outside, curtains over basement windows, mail slots in garage doors. Setting aside questions of housing code enforcement, San Jose needs the census to find these residents, too, if the city is going to get its full share of the political power and federal resources tied to the national head count.

Two years out from the census, cities are scrambling to avert an undercount they fear could be unusually large for reasons both political and practical. Across California, the housing crisis means that even more households are doubling up in existing homes and occupying illegal ones. In Houston, many families remain displaced by Hurricane Harvey. In New York, the city has permitted so much new construction that the Census Bureau — compiling address lists now — may miss thousands of units to be completed between now and 2020.

Cities must find all these households before they even get to the second challenge: persuading the people who live in them, many of them immigrants, to participate in the census.

“For us, this is a very big deal,” said Mayor Sam Liccardo of San Jose. City officials believe the 2010 count of 945,942 residents missed as many as 70,000 residents, costing the city about $20 million annually in lost resources. And that happened with an administration in Washington that was perceived as more immigrant-friendly, Liccardo notes.

“Rumors of ICE raids are on Spanish-speaking radio every other day, and you’ve got this enormous fear from residents about talking to the government,” Liccardo said. “You do everything you can to communicate to people, ‘Hey you’re safe with the city, please talk to us.’”

He and other mayors with large immigrant populations fear that President Trump’s tough talk will make it even harder in 2020 to count immigrants — legal and undocumented, often in the same household — who are hard to reach in any census. The Justice Department has also requested that the Census Bureau add a question about citizenship status that the U.S. Conference of Mayors and the National League of Cities have protested.

“We don’t need the federal government trying to define who’s in the community,” said Mayor Catherine Pugh of Baltimore. “This is about bodies, it’s not about whether you’re an immigrant.”

In Houston, the city suspects that many immigrant households devastated by Hurricane Harvey never reached out for government assistance, and those programs offered tangible benefits to residents whose homes and cars had been flooded.

“If you are reluctant to reach out because of your fear that ICE may show up, for fear of being deported, then how do you think people are going to feel when you’re asking them to go online or to respond to an enumerator that’s knocking on your door to fill out a census form?” Mayor Sylvester Turner of Houston said. “They’re going to be apprehensive.”

In San Jose, the city will rely on community volunteers this spring to scour neighborhoods where it suspects many families are doubled up or living in unpermitted housing. On the street with the beige garage conversion, Almeida could point to a clue on nearly every property. Peeking over a fence, he spied another garage with a satellite dish mounted outside. One home had an R.V. that looked to be permanently stationed in a large carport. Across the street, a home zoned for just one unit had a second address posted outside. The home next door had two satellite dishes on the chimney and a third on the garage.

This spring, volunteers will use a texting app the city tested in December to identify these and similar units. The city will then flag them on the Census Bureau’s master address list for San Jose. Almeida vows that the city department in charge of building code enforcement will never see these address notes, and the Census Bureau requires confidentiality from the local officials who do access them.  A nonprofit founded by the former New York mayor Michael Bloomberg, Cities of Service, is hoping to spread the tool to other cities that will be receiving their address databases from the census in the coming weeks.

In New York City, half a dozen workers in the planning department have been similarly canvasing neighborhoods for the last 15 months. Ahead of the 2000 count, the first time the Census Bureau allowed cities to review their addresses, New York found 439,000 units the bureau was missing — the equivalent of 13 percent of the city’s housing stock — mostly in illegal basement, attic and garage apartments revealed by extra doorbells and mailboxes.

Going into 2010, the city found an additional 200,000. This year, New York expects to add roughly 100,000 units, this time mostly new, legal housing the census hasn’t yet recorded. That could represent a quarter of a million people. New York State is already expecting to lose one congressional seat in reapportionment after the census, as the population of Sun Belt states continues to grow much faster. A drastic undercount could cost New York a second seat.

“People forget it is an enumeration of the population, but it’s an enumeration of the population in housing units and in group-quarters facilities,” said Joe Salvo, the director of the New York City planning department’s population division. “Essentially, everyone needs to be put down on a map. Everybody needs a recognized address.”

These surveys that cities are rushing to complete now are the closest they’ll get to conducting their own counts to fact-check the official one. How will they know, then, if the numbers look right after 2020?

“You know it anecdotally; you talk to people and say, ‘Hey, did you answer the census?’” said Mark Stodola, the mayor of Little Rock, Ark. He fears that in 2010, out of a metropolitan area of 725,000, about 30,000 Hispanic residents in the region were not counted. “If five out of 10 people tell me that they didn’t answer it, that tells me we’ve got a huge undercount.”

Emily Badger is a reporter with the New York Times. Copyright 2022, The New York Times.