LAS VEGAS — The swanky, billion-dollar casinos of Las Vegas are bedecked with shining towers, neon signs and eye-popping extravagance. But beneath the glitter, hundreds of homeless people live out of sight, in the dark, in a network of stormwater tunnels running below the city.

When census takers tried in September to count the nation’s homeless for the 2020 census, safety concerns prevented them from venturing into the tunnels.

The tunnels offer just one example of the difficulty in counting the portion of the homeless population that does not stay in shelters. A half-dozen census takers around the country told The Associated Press they experienced problems that could cause the homeless to be undercounted — a situation that may cost some communities political representation and federal money.

America DePasquale, who lived in the tunnels from May 2018 until she moved into a detox facility last month, said she never saw census takers visit the area underneath the Las Vegas Strip.

DePasquale said she does not blame census takers for not attempting to enter the tunnels, but she said it might have helped if they had tried to go with community advocates who make frequent visits below.

“It takes somebody of a certain strength to go down there just regularly, ” she said. “But I also find it kind of appalling that they wouldn’t go deeper and at least even try.”

The count of the unsheltered homeless was originally scheduled for last spring, but the Census Bureau delayed it until late September because of concerns about the coronavirus. The bureau identified 33,000 homeless camps for census takers to visit.

The Government Accountability Office warned this month that the delay in the homeless count could affect the quality of the census data.

“Because people who experience homelessness are more likely than people who are housed to be members of minority groups, especially African Americans and Native Americans, the undercount contributes, modestly, to the serious undercount of minorities and poor people,” said Beth Shinn, a professor at Vanderbilt University who researches homelessness.

The Census Bureau said the unsheltered homeless count is designed with the safety of census takers and those being counted in mind.

The agency’s once-a-decade count helps determine $1.5 trillion in federal spending annually and how many congressional seats each state gets.

Census takers would face a lot of challenges if they tried to enter the tunnels on their own to interview residents, said Paul Vautrinot, who leads a nonprofit that provides housing, counseling and other services to several hundred people living in the tunnels.

Drug use, rats and human waste are common sights.

“It’s a very daunting task to go walking down there,” said Vautrinot, who lived in the tunnels from 2011 to 2014. “There are moments that you go down there and the hair on your arm raises up.”