A "person of interest" was taken into custody after the shooting at Don Carter Lanes on East State Street, Rockford Police Chief Dan O'Shea said during a news conference.
WATCH: Rockford Police Chief Dan O'Shea give latest on shooting
6 shot, 3 killed in apparent random shooting at Don Carter Lanes bowling alley in Rockford, IL
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O'Shea said he did not think any officers fired their weapons, but the shooter was active when police arrived on the scene.
Police said a 37-year-old man was in custody in connection with the incident.
Two teenagers were among those shot, O'Shea said, but he did not know their ages.
RELATED: Chicago weekend gun violence leaves 12 shot, 3 killed across city
Rockford police asked the public to avoid the area during the following investigation in a tweet about 7:15 p.m.
O'Shea said Rockford police received calls for shots being fired at the bowling alley at 6:55 p.m.
Republican U.S. Rep. Adam Kinzinger, whose district includes Rockford, tweeted he was "Praying for the victims and their families tonight after the heinous attack in our community."
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Rockford is about 80 miles northwest of Chicago.
ABC News and Associated Press contributed to this report.