Chicago's Office of Emergency Management and Communications on Thursday evening said no credible threats have been made against the city.
Still, officials are asking citizens to report any suspicious activity they may witness.
"While there is no credible threat to the city at this time, we remain vigilant," said OEMC Executive Director Gary W. Schenkel in a statement. "We encourage residents to also remain alert and call 911 if you witness any suspicious or unusual activity."
New York City and Washington, D.C., meanwhile, are ramping up security after the Department of Homeland Security earlier in the day disclosed a "credible" threat timed for the tenth anniversary of the September 11, 2001, attack on America.
In Chicago, Amtrak is stepping up security at Union Station by increasing its canine explosive detection unit and other security measures. Across the country, Amtrak has increased passenger and bag screenings and expanded police patrols.
Stations also have posted signs that read, "If you see something say something. Hopefully it's nothing."
Commuters Friday morning told NBCChicago they still feel comfortable taking public transportation, and while they will remember the 9/11 events, they also will be aware while traveling.
"It's a good day to remember what happened but also not to let it stop our day," said Antonio Johnson.
"I'm certainly going to remember everything that happened," said Steve Wright. "I'll never forget. So I'm going to stay vigilant and make sure to stay safe, but you can't change your life for it."