Forty-five thousand people representing all 50 states and over 129 country will run and an estimated two million will line the course to watch.
The marathon will start in Grant Park and runners head out on Columbus Drive shortly after 7 Sunday morning.
They will travel as far north as Addison, as far west as Damen Avenue and as far south as West 35th Street before they turn back north and end up back at Grant Park.
As a result of the Boston Marathon bombings, this year there are quite a few security measures in place, but nothing, say organizers, that should detract from the runners' experience.
It's a pre-race tradition. The big pasta dinner athletes indulge in to carbo load the night before the marathon. Saturday night, at the Hilton, hundreds of runners came together to eat and measure up their training to their competitors.
"I'm ready," said runner Debbie Robinson. "I've been training for at least 20 weeks. I did my last 20 mile run two weeks ago."
In Grant Park, last minute preps are still going on and all the streets leading into the race area are already closed off. Four distinct entrances off of Michigan Avenue have been designated for runners and spectators Sunday, who will, unlike previous years, have to go through security checkpoints before making their way to their corrals.
Saturday night, runners were still trying to get their bearings.
"We're just taking a look at the bag and security points especially for this year since I don't think they had that last year," said Mary Scott.
Executive race director Carey Pinkowski had some advice for those still unsure about the protocols for Sunday.
"Obviously we have some more enhancements this year, so give yourself more time to get to the race area, to get to the volunteer or spectator location," he said.
Back at her downtown hotel, Lisa Seeper, lays out her things for Sunday. Security concerns are the last thing on her mind. It's not only her first marathon. She's running it just seven months after suffering a stroke.
"The first words out of my mouth when they brought me into the hospital were, 'I signed up for the Chicago Marathon, I'm going to be able to do it, right?' And they were like 'Yeah, yeah, sure,'" she said. "But I told my physical therapist, 'before I leave I'm going to be running down these halls,' and you know what? I was."
Seeper credits coach Denise Sauriol for getting her to the start line. Sauriol was there for her Saturday night, with some advice for anyone thinking of running a marathon.
"The marathon, first you have to want it and then you have to have someone by your side helping you, and with the right training, if you have that hunger you will get through it," Sauriol said.
Unlike previous years, spectators will not be allowed to run with friends or family at any point during the race.
Also, for those wanting to gain access to the finish line area or post-party area, they will only be able to do so after 9 a.m.
