They come from such places as Africa, Asia, Latin America and Eastern Europe because of the promise of the "American Dream."
But many of them find themselves in the clutches of a nightmare of prostitution, forced labor, domestic servitude and abuse.
They are victims of human trafficking, a modern-day form of slavery that is also a lucrative, multibillion dollar global industry. It is the second largest criminal industry in the world, according to the U.S. Department of Health and Human Services.
And while human trafficking is more prevalent overseas, the U.S. State Department estimates that 18,000 people are trafficked into this country each year. The clandestine nature of the industry, however, makes exact figures difficult to pinpoint.
"There are no scientific census counts, and victims ... do not typically stand out in the open and raise their hands," said Ambassador John Miller, who heads the U.S. Office to Monitor and Combat Human Trafficking in Washington D.C. "The estimate also does not count internal (domestic) trafficking."
In Illinois, the number of trafficking victims is similarly elusive.
"We don't know how big the problem is, and this runs parallel to the national problem," said Katherine Kaufka, supervising attorney for the counter-trafficking program at the Chicago-based National Immigrant Justice Center. "We have served over 60 victims in last three years, but the numbers are higher."
The government defines human trafficking as the recruitment, harboring, transportation or obtaining of someone through the use of force, fraud or coercion for the purpose of involuntary servitude, peonage, debt bondage or slavery.
"We are a transportation hub, we are an agriculture state in need of cheap labor, and we are a state with a higher percentage of immigrants and immigrant communities," said Greg Diephouse, of the Illinois Department of Human Services. "It is easy for a victim to land in Chicago and go under the radar."
Salvador Cicero, a Chicago attorney and director of the Ecuador Anti-Trafficking Persons Project, agreed.
"Most people don't realize it goes on right under our noses in Chicago."
Cicero recalled a young, middle-class Latino male who was kicked out of his home by family members when they discovered he was gay. With no place to stay, the youth became prey to sex traffickers.
"This is not just a poor person or immigrant issue," Cicero said. "It could happen to anybody."
Trafficking in sex slaves has generally received the most media attention. However, trafficking in forced labor and domestic servitude makes up for half of Kaufka's cases.
"We have rescued victims all over the state," Diephouse said. "This is not just an issue for Chicago, but for all of Illinois."
In January, the Trafficking of Persons and Involuntary Servitude Act went into effect in Illinois. At the time the bill was signed in June 2005, the state also launched the rescue and restore campaign -- a partnership between the U.S. Department of Health and Human Services and law enforcement, social service, health care and advocacy organizations across Illinois.
The campaign hopes to reach out to potential victims with 24-hour hotline information in a variety of languages and educate potential first-responders, such as health care workers and law enforcement, about trafficking.