Updated

Hoisting American flags into the air, tens of thousands of immigrants from the Chicago area marched downtown in a display of support for immigrant rights as a bill to stiffen border enforcement awaits action in the U.S. Senate.

Many took up enthusiastic chants like "Si, se puede (Yes, it can be done)" and "La raza unida nunca sera vencida (A people united will never be defeated)."

The mostly Latino marchers Friday descended upon the plaza across from the federal courthouse, where they listened to speeches backing pro-immigrant legislation.

"Raise those American flags!" shouted U.S. Rep. Luis Gutierrez, a Democrat. "This is our country, and this is where we will stay."

Police estimated that more than 100,000 marchers came from all over the Chicago area, many carrying — or wearing — Mexican and American flags. The protest was spirited, but peaceful, and there were no reported arrests or incidents.

The legislation, already passed by the U.S. House, is billed as a border protection, anti-terrorism and illegal immigration control act. It includes such measures as enlisting military and local law enforcement help in stopping illegal entrants and authorizes the building of a fence along parts of the U.S.-Mexico border.

Gov. Rod Blagojevich addressed the crowd in Spanish, telling them he is the son of immigrant parents and understands their issues.

The Democrat's proclamation that "ustedes no son criminales. Ustedes son trabajadores" ("You are not criminals. You are workers") brought loud cheers.

Abigail Marquez, 35, said she came to the rally with her husband and teenage son to express her support for Latino issues. The native of Guadalajara, Mexico said she did not expect so many people to participate in the march, organized by dozens of activist groups.

"I had no idea. There are just so many people here," she said in Spanish. "I feel very happy because it shows that we are all united."

The march began at noon at a park several miles west of the downtown Loop business district. Hours later, marchers still thronged the Loop, clogging streets and tying up traffic. By early evening, traffic had returned to near-normal levels, police said.

Abel Nunez, associate director of a social service agency that was one of many organizations spearheading the event, said the goal was "to demonstrate to people that immigrants are here and we contribute to this country."

The Illinois Minuteman Project, affiliated with a national volunteer civilian border patrol group, held a news conference before the march began.

State director Rosanna Pulido said she does not want to see Chicago become a "sanctuary city" for illegal immigrants. Nationally, the illegal immigrant population has grown from about 8.4 million in 2000 to nearly 12 million, according to a new report.

"There are 14 million underemployed Americans," she said. "Don't they have the right to have a better life and support their families? Let's give them an opportunity because this is their country."