South Carolina, a state with historically few illegal immigrants, saw a 1,000 percent increase in their numbers from 1990 to 2004.

"Are we going to run this work force off?" asks the Republican lawmaker, quoting constituents. "And what are you going to do about broken borders?"

With 55,000 undocumented residents, South Carolina ranks far behind the nation's leader, California. But the issue is boiling throughout the country as illegal immigrants make their way to more cities and states than ever.

The Senate is debating legislation this week that would tighten border security while enabling illegal immigrants to eventually become citizens.

The Pew Hispanic Center, a research organization in Washington, estimates there are as many as 12 million illegal immigrants in the United States, though researchers acknowledge they are difficult to count. Other organizations have put the number at 11 million, but all agree the total is rising quickly.

Illegal immigrants are more likely than American citizens to hold jobs but less likely to have high school diplomas. They tend to be younger, and many have children who were born in the U.S., making the kids citizens.

Less than half fit the profile of young men sneaking across the border to find jobs and send money back home to their families. Today, most bring their families with them, according to an analysis by the Pew center.

"There's about 6.5 million adults who are in families, either couples or couples with children, and there's another 2 million children," said Jeffrey Passel, a senior research associate at the center. "The vast majority of this population is families."

In 1990, almost half lived in California, the Pew analysis said. By 2004, California's share had dropped to about a quarter, even though the state's illegal population had grown from 1.48 million to about 2.45 million.

They are moving to states like North Carolina, Iowa, Ohio and Georgia as they seek jobs and establish communities. North Carolina has nearly 16 times the number of illegal immigrants it had in 1990, the Pew analysis said. The state had 390,000 in 2004, the most recent state numbers available.

About a quarter of them arrive in the United States legally and simply overstay their visas, Passel said.

"We have about 30 million people per year come here on temporary visas, either tourists or visitors for business," he said. "With 30 million folks coming here a year, a very small percent who stay adds up over the years."

Adult men make up the largest share of illegal immigrants, followed by adult women and then children.

Many families include relatives of differing immigration status. Nearly two-thirds of the children were born in the United States.

Illegal workers make up about 5 percent of the U.S. labor force. More than nine in 10 males illegally here are in that labor force, compared with 83 percent of men born in the United States.

Illegal immigrants tend to be younger than American workers, which helps explain why they are more likely to hold jobs, researchers said.

Female illegal immigrants, however, were less likely to work than their American counterparts, perhaps because most have young children, the Pew analysis said.

Illegal immigrants are concentrated in construction, agriculture and cleaning jobs. They make up 36 percent of all insulation workers, 29 percent of agricultural workers and 29 percent of roofers.

The Center for Immigration Studies, which advocates restricting immigration, recently issued a report saying that immigrants compete for jobs with less-educated Americans, especially high-school dropouts.

About half of adult illegal immigrants have not graduated high school, the Pew analysis found. About a third have less than a ninth-grade education.

About a quarter of illegal immigrants have at least some college, with 15 percent holding at least a bachelor's degree.

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On the Net:

Pew Hispanic Center: http://pewhispanic.org/

© 2006 The Associated Press