Organizers have instituted baggage checks for runners and fans as well as restricting access to key points along the 26.2-mile route that winds through the downtown Loop, passes Lincoln Park Zoo and neighbourhoods such as Little Italy and Chinatown.
Chicago's race is part of the World Marathon Majors series, which consists of Boston, Berlin, London, New York and Tokyo.
Enthusiasm in Chicago has not been dampened by the bombing in Boston, which killed three spectators and injured scores of others. Sunday's race is sold out, with 45,000 participants registered, along with the usual 12,000 volunteers signed up to pass out water and assist at aid stations along the route.
Attendance is expected to be similar to the past, when some 1.7 million fans line the route encouraging runners.
The new measures will be evident before the race starts as runners must pick up their own participant packets, which includes their event bibs and timers. In previous years, someone else could pick up the packs for the runners.
The participant packs will include a clear plastic bag that runners must use for their race-day supplies, another new requirement. Marathon organizers said they will not accept any other bags at gear checks.
Spectators and runners entering Grant Park - the public area where President Barack Obama held his 2008 election victory rally and where the race starts and finishes - will be funnelled to four security points.
All bags anywhere along the race route could be screened by security officials, organizers said. Although it is not a new restriction, grandstands surrounding the start and finish area will be closed to the general public, with tickets distributed in advance by organizers.
Police will step up the use of bomb sniffing dogs during the race as well as trying to keep the entire route of the race area clear of unattended baggage.
Chicago Police Department Superintendent Garry McCarthy said he had multiple conversations with his Boston counterpart in the run-up to the marathon.
Chicago organizers declined to say how many security personnel will be working at the race, or how many agencies will be involved, but noted that they have coordinated with the Department of Homeland Security, the Department of Justice as well as the Secret Service.
"I do feel like they are doing everything they can" on security," said Jenn Wisegarver, who is registered for the race and also ran the Chicago marathon last year.
Spectators are more likely to be on the lookout for potential risks, said Lou Marciani, director of the National Center for Spectator Sports Safety and Security at the University of Southern Mississippi.
"We all become first responders, reporting and responding to potential activity." Marciani said.
The New York City Marathon scheduled for Nov. 3 also is tightening security, including searching the bags of fans.
Other sporting events in the United States are increasing security after Boston.
The National Football League's new rules stipulate that bags brought into stadiums for games must either be clear or small clutch bags, approximately the size of a hand. The move caused some complaints from fans, particularly women who carry larger purses, after they were announced.
Marathons pose a particular challenge due to the long route as well as the use of public streets.
"It is impossible to effectively blanket with effective security coverage a route of that distance," said Patrick Brosnan, founder and chief executive officer of Brosnan Risk Consultants, which works with sports teams and venues. "As always, you say a little prayer."
- Sports & Recreation