The first wave of runners was scheduled to take off at 8:30 a.m. in Grant Park.
The race, which is organized by Bank of America, is the world's largest timed 8K race.
The race course winds through downtown back to Grant Park, where the traditional post-race party kicks off at Buckingham Fountain.
The Shamrock Shuffle draws participants from well beyond the Chicago area.
"It is a very well run race. We have great support from our city agencies, our corporate partners. Our charities use this as a great opportunity to promote their efforts as we go through the year. It is a great team effort, a great celebration of running in Chicago, a great venue in Grant Park, and a great tour of the downtown area," said Executive Race Dir. Carey Pinkowsk said.
As participants rushed to register, organizers reached their limit by March 12, weeks ahead of the race.
Barricades were in place early, and the weather appeared to be cooperating. Some runners said early Sunday that the cool mist in the air would help them run a better race, a big plus compared to warmer temperatures last year.
This year's male and femal winners were Abdelazziz Atmani of Indiana and Julia Lucas of Portland, Ore., respectively.