The McHenry County Sheriff's Office said their deputies responded to reports of an aggressive dog fight at West Heumann Drive and Stilling Boulevard in McHenry.
Several people were injured in the fight and its aftermath, police said, including a deputy who was bitten.
One dog was shot by a deputy. The other dog, who police described as aggressive, remains on the loose. Both dogs were brown pit bulls, the sheriff's office said, including the one still on the loose.
The sheriff's office asking people to stay in their homes for their safety, and to report any sightings of the dog to the sheriff's office at 815-338-2144.