A funeral was held for Officer Jason Gallero in west suburban Westchester.
The 22-year veteran died last Thursday after collapsing during a colors run at the sheriff's training facility.
The 5K race welcomes new recruits to the police force and salutes law enforcement who, like Gallero, died in the line of duty.
Gallero's fellow officers said he was an incredible leader who died doing what he loved.
"If you could have heard their roads when he came out of that car to join them in the run it was amazing," said Tom Dark, Cook County sheriff. "I mean he was the whole package he's so sorely missed already."
The 45-year-old Gallero left behind a daughter and other family members.