According to the Chicago Office of Emergency Management and Communications, there is no known threat to Chicago at the moment. Safety measures have been stepped up throughout the city as a precaution.
"We are closely monitoring events as they unfold in Boston and the City of Chicago's public safety departments are actively communicating with our law enforcement partners both locally and throughout the country. At this time, there is no known threat to Chicago," OEMC officials said in a statement. "We remind first responders, as always, to use caution when responding to suspicious persons or activity."
As Chicago Blackhawks fans streamed in to the United Center, Chicago police patrolled the area. It was a more significant presence than usual in response to the deadly explosions at the Boston Marathon.
The fans said they appreciate the extra security.
"I think it's a great idea," Blackhawks fan Dan Panek said.
Gov. Pat Quinn says he has reached out to the Illinois Emergency Management Agency after deadly explosions near the finish line of the Boston Marathon.
He says nothing suggests there any connections to Illinois or Chicago. But the Chicago Democrat says Illinois must be on the alert.
Quinn characterized the explosions as "a potential terrorist incident" but said more facts need to come out.
Quinn says he has directed all state public safety agencies, including Illinois State Police, Illinois Department of Military Affairs and the State Fire Marshal to be ready to assist and remain vigilant. He also asks Illinoisans to report anything suspicious.
"The running of the Boston Marathon and Patriots Day are time-honored traditions. While the details of today's tragedy are still unclear, one thing was immediately known: the patriotism and professionalism of public servants and first responders. Our hearts go out the first responders, runners, volunteers and spectators in Boston today," Chicago Mayor Rahm Emanuel said in a press release.
Commuters saw increased security on Metra and Amtrak trains in the Chicago area Monday night.
"In response to recent events, you may see an increased police presence at Chicago downtown terminals and onboard trains. As always, should you see something you believe unusual or out of the ordinary please notify a conductor or a uniformed Metra police officer," Metra officials said in a statement.
Security is being tightened at airports across the country. A government official told ABC News that security has been beefed up at Boston's Logan Airport especially for outgoing flights.
Runners from Illinois witness event
About 950 runners from Illinois were registered for Monday's Boston Marathon.
The Bank of America Chicago Marathon issued a statement, "We are deeply saddened by today's events, and our focus is on the victims and their families."
Fleet Feet Sports in Chicago had 86 runners taking part in the marathon and the owner says they've all been accounted for.
As passengers at O'Hare watched the events in Boston unfold on television, Chicago-area runners are starting to make their way home Monday night.
Brad Moates and Andre Bennatan finished the race an hour before the explosions. They were eating a slice of pizza close to the finish line when they heard what sounded like a cannon..
"We were right near finish line 200 meters away. Ten-fifteen seconds later another went off, holy hell, runners were running in the opposite direction," Moates said.
It was chaotic because no one knew where to go or what was next, according to Moates.
"Ambulances were coming everywhere people in tears crying took taxi to airport," he said.
Runner Patrick Ford was on his way to the airport and he knew something was wrong when he saw several police cars and ambulances going toward the finish line.
"It could have just as well been me, I didn't have a good running day, but it would have been worse right there," Ford said.
Arlington Heights Mayor-Elect Tom Hayes ran his ninth Boston Marathon Monday. He and many other runners say despite what happened they will run it again.
"It's not going to change my approach," Hayes said.
Runner Dave Shannon from west suburban Elmhurst had just finished the race when the blasts occurred and he told us what he witnessed.
"I was heading back toward the starting line just to get to the family meeting area, so I was looking right down the street from about two-and-a-half blocks away, heard the explosion, saw the ball of smoke, and seconds later, the second explosion, second ball of smoke," he said. "And there was fear in people's eyes. It was clear that this was not part of the festivities for the end of the race. Everything went silent."
Shannon said his family members felt the ground shake during the blast.
The Associated Press contributed to this report.
