The wheelchair race gets underway at 7:20 a.m., with the first wave of runners schedule to start at 7:30 a.m.
To be ready for the starting line, runners Saturday night hit the buffet line.
"This is plate number two," said Sante Kotturi. "I'm working my way through it, so I'll have lots of energy (Sunday)."
The annual pre-race dinner at the Hilton on South Michigan served up three kinds of pasta, salad and plenty of dessert.
There was even a bar to calm those marathon eve nerves.
"I'm hoping I can sleep enough," Karen Kotturi said. "I don't know if I'm going to be able to sleep. I'm kind of excited and nervous."
Odino Steffan is here all the way from Italy.
"Chicago is a very clean city, I like it," he said.
For many runners, Sunday night was also about spiritual nourishment.
The pews were full at Holy Name Cathedral for the annual blessing of marathon runners.
"While I'm running I am talking to God all throughout, absolutely," said Andrew Cubria. "To be there and to be available and to be healthy enough to even finish 26 miles is a blessing in and of itself."
Many of the 45,000 registered runners are racing for a cause.
Ashley Kumlien, whose mother was diagnosed with multiple sclerosis, ran coast-to-coast two years ago to raise money for MS Research.
Sunday, she'll be raising thousands more ror her mother and many others.
"They always have a great outlook on life, so I figure if they can be positive and remain focused through such an adversity...," Kumlien said. "They have their own endurance event, living with MS, so I can run and do it for them."
Though temperatures at the start of the race could be in the thirties, few seem fazed.
"It'll work really well for our elite athletes," Pinkowski said. "I think they're going to be energized. All the great performances in the history of the marathon have come in cool weather."
Parking restrictions go into effect at 1 a.m. Sunday morning. Vehicles will be ticketed and towed, as streets along the race route closed from 7 a.m. to 3 p.m.