Dunn was a 46-year-old father of two children, a history buff with a love of the outdoors, and a loyal community servant. Those who knew him say they're not surprised that he died while apparently protecting someone else.
On Wednesday, flowers sat at the intersection where Thomas Dunn Junior lost his life.
"It's hard to even express in words sometimes how much we're going to miss him. It's very, very hard," said Patt Dunn, victim's brother
Dunn, who went by his middle name Jim, worked as a teacher's aide at a school for kids with autism and other special needs.
"It didn't matter who you were. It didn't matter how you were. He was the same with every student, every staff member. He was a person who cared deeply," said Jon Klavohn, principal, Camelot Therapeutic Day School.
On Monday afternoon, he was doing what he often did: teaching a student a life lesson by walking him across the street to buy a soda.
Police say a public transit bus hit Dunn as it was turning left, barely missing the student. Investigators are now looking into initial witness statements that Dunn pushed the child out of harm's way.
"Knowing Jim Dunn, it wouldn't be surprising had he done that. If you know Jim at all, that would be an instinctive reaction that he would have," said Interim Chief Greg Kunce, Bourbonnais Police Department.
"Doesn't surprise me at all because that's the type of person he was. He would always put himself out to protect somebody else. That's the kind of thing he did," said Patt Dunn.
To protect and serve was something Dunn knew well. He was a nearly 20-year veteran of the Bourbonnais police auxiliary unit, volunteering to help the village during festivals and events. And he was among the first responders during one of Bourbonnais' darkest hours, the fatal Amtrak crash in March of 1999.
"He's the first one through the door if you call to muster up some people. He's the first one to arrive, and what do you need?" said Kunce Dunn is survived by his two children. Relatives and friends say his death speaks to how he lived.
"He's a true hero if in fact it's determined that he pushed that child out of the way. That's a selfless act that he would have done," said Kunce.
In Bourbonnais, Dunn's family is well known. His father, Thomas Dunn Senior, is the head of the police auxiliary unit, and his brother Pat is the village attorney.
Illinois State Police are investigating what happened. It could be a few weeks before they issue their report.