Rockford Police doled out 459 arrests for drunk driving last year, according to a recent study.
Decatur came in second with slightly more than 400 arrests. Chicago is not factored into the evaluation due to its size.
Meanwhile, Illinois State Police saw a significant drop in intoxicated driving arrests.
Rockford Police Chief Dan O'Shea said his department stepped up its efforts after 16 traffic fatalities in 2015.
"There's crashes, crime or complaints, if you will," he said. "Those three things drive how we push our traffic enforcement."
O'Shea said he doesn't believe the city has an issue with intoxicated drivers, but urges people to not take a risk with impaired driving.
"There's plenty of ride-share services or cabs out there," he says, "and it's not you on the road; it's you and everyone else on the road."
Rockford Police Sgt. Benjamin Boeke adds that it will take widespread community awareness to help reduce impaired driving.
Boeke said Rockford Police will be extra vigilant through the 4th of July in its enforcement efforts.