U.S. Census Bureau Director Robert Groves emerged from the caravan Monday with a message: You can trust us.
His entrance didn't convince everyone.
"When they saw the uniforms of the sheriff's department? Some got scared," said Maria Aguirre, a longtime resident of San Carlos, which she said has about 300 people.
That anxiety among immigrants illustrates one of the biggest obstacles facing the Census Bureau this year: persuading those residents most afraid of the government to participate in the decennial count.
The stakes are high. An accurate head count in the 2010 census could mean millions more in federal dollars for a community or redrawing legislative boundaries. Undercounting could leave states shortchanged.
Border counties, flush with residents fearful of being turned over to immigration agents, are historically among the most undercounted. The Census Bureau ranks Webb County - where Laredo is located - among the nation's hardest-to-count areas, joining a list that includes rural places in Alaska and South Dakota.
Speaking to about a dozen colonia residents, many of whom only speak Spanish, Groves tried to allay their fears. He stressed that census data will be kept confidential and not turned over to other agencies.
"If the president asked me for your census form, I can say 'No, you can't get it,'" Groves told the crowd. "If I violate that law, I can go to prison."
Groves visited the colonia with Democratic U.S. Rep. Henry Cuellar, who said his district, which includes Laredo, lost more than $55 million in federal dollars during the last census because of undercounting.

