It's places like that, large gatherings where security will be top priority unlike any year before.
"We are going to ask you to be ever-diligent and pay attention to what's going on around you," said Scott Friedlein, Emergency Services Coordinator for the marathon.
That lesson wasn't originally on the agenda at training sessions for marathon volunteers. But for Friedlein, it immediately became the most important.
"While we think our risk is relatively low, it's still not unheard of that this could happen here. So we're going to take whatever precautions we need to take," he said. "So my first phone call was to Champaign (police department) saying, 'hey, for our next meeting I'd like to have an official request to appropriate an official who is involved in terrorism to talk about this, too.'"
"It's definitely out of the ordinary, and you do always worry about copycats crimes," said first time volunteer Dennis Matthews. "There's not a lot of security around these races, especially over a course of 26 miles."
150 police, firefighters, medical personnel and public works employees help on race day. Friedlein says it's possible even more will line the routes this year. But he's also relying on thousands of volunteers to keep an eye out.
"Memorial Stadium, the start line, finish line, those types of things, will become areas that we're going to really remind them look for suspicious devices or packages," he said. "Or things that just don't look normal, or look for behaviors that don't look normal."
It might not be exactly what volunteers expect to hear, but organizers insist the show must go on.
"We're not intending to cancel the race," said race director Jan Seeley. "We will do everything to make sure it's a safe event. But I think cancelling is what people want you to do."
"I'd hate to see us back off of showing that expression of community and that sense of pride in what this event is really all about," said Friedlein.
Wednesday, Seeley and Friedlein will have an official security meeting. Champaign, Urbana, UI, and state police will be there. A terrorism expert will also attend.