With the toll of a single bell outside a River North firehouse, city leaders and first responders lined up at attention to remember the thousands of lives lost.
A massive American flag was hung proudly between two Chicago fire trucks.
"It's so important the next generation knows the sacrifices that were made and how it's relevant today," 2nd Ward Ald. Brian Hopkins said. "The first responders today risk their lives every day, just as they did on 9/11. They never know what's going to happen when they come to work today."
SEE ALSO | US marks 24 years since deadly 9/11 terror attacks
At Chicago's Union Station, nearly 2,000 volunteers worked hand-in-hand to pack meals for the Greater Chicago Food Depository.
"It's inspiring to me to see all the people that have taken time off work, time out of their busy schedules to come here and make a difference and to turn this day into something that really honors and turns it into something positive," said Camerin Mattson, a spokesperson for Greater Chicago Food Depository.
Organizers said they hoped to pack 500,000 meals by the end of the day.
"We lost 358 colleagues on 9/11 in the World Trade Center," said volunteer Sarah Stephans, who works for Marsh McLennan, a global services firm. "We've been coming together for about a decade around the month of September for Days of Giving."
"Remembering the solemn memory of those who lost their lives that day is important on the most brutal attack on our nation since Pearl Harbor," 34th Ward Ald. Bill Conway said.
The city of Aurora held its annual memorial ceremony at about 7:30 a.m. at the Aurora fire station on Broadway.
RELATED | September 11 coverage from WABC-TV Eyewitness News in New York over the years
Chicago pays tribute to 9/11 victims
Down the street, they have a 9/11 exhibit featuring a centerpiece with a model of the World Trade Center buildings in New York, surrounded by two steel beams recovered from what was left of the buildings.
In Hoffman Estates, there is a permanent memorial outside the police department, and some on Thursday reflected on vivid memories of 9/11.
For some, it seems like yesterday. For others, the terrorist attacks are something they've read about in history books.
In Palatine, first responders marched from the fire department to the Sept. 11 memorial in the center of downtown. It was a solemn occasion.
In Arlington Heights, students at Hersey High School stepped up to raise money and awareness of veterans' mental health, carrying backpacks up steps, just as New York firefighters did.
"What all the firefighters and first responders went through, extreme," Andrew Maciron said.
All of the students were not alive yet Sept. 11, 2001. Most of what they know of it comes from their parents and teachers.
"Any time I see news about it or video, it's like, I can't believe that happened," Ndidi Iwuagwu said.
Teacher Jim Miks helped organize a display of drawings of post-9/11 heroes from Illinois. All the students at the school also volunteered for a day of service to honor those who died.
"To me, it's very important to teach the kids about being good to each other, not cynical, positive," Miks said.
"We think of our country as very divided, but that day really showed us how we can come together and be there for each other," Natalia Strugacz said.