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Police were typically quiet about it on Thursday but chances are the mood was anything, but calm in some of the drug-infested neighborhoods of North Chicago and Waukegan.

That’s because teams of investigators descended on those neighborhoods Thursday to serve dozens of arrest warrants, which were the result of an extensive probe conducted by the Lake County Metropolitan Enforcement Group.

Lake County State’s Atty. Michael Waller said authorities will detail what was described only as a “major undercover investigation” during a press briefing scheduled for 9:30 a.m. Friday at the Waukegan Police Department.

Law enforcement sources, though, say it was a 3- or 4-month investigation focusing on street-corner drug dealers. More than two dozen arrest warrants were issued for drug-related offenses, mostly for selling small amounts of cocaine.

The Metropolitan Enforcement Group, or MEG, is a special task force comprised of detectives from a number of area law enforcement agencies, including the Illinois State Police.