The shooting took place at Don Carter Lanes just before 7 p.m. local time, according to the Rockford Police Department, ABC News reported.
A suspect, described by police as a 37-year-old white man, was taken into custody.
"When officers arrived on the scene, the shooter was still in the building," Rockford Police Chief Dan O'Shea said at a briefing. "No officers fired their weapons we know of at this point, but the individual that we believe is responsible, and the only individual we believe at this point to be involved, we may have in custody. But it's still to be determined."
The state attorney's office has been notified and the investigation is ongoing.
At least two teenagers were among those shot, O'Shea said, but he couldn't provide further details on the people who were injured or killed.
"We're working with the business owners, they are on scene providing all cooperation they can to help us," O'Shea said.
Police said some people were shot outside the building and some inside.
Rockford, one of the largest cities in Illinois, is located about 90 minutes outside Chicago and two hours southwest of Milwaukee.
ZZ/PR