Stacy Peterson, 23, disappeared in Oct. 2007. She was former Bolingbrook police sergeant Drew Peterson's fourth wife.
The search in the Hammel Woods area is not related to any new leads, but is part of periodic searches held in the case, according to the source.
Stacy Peterson's cell phone showed activity in the Shorewood area around the time she disappeared. The search on Monday wrapped up around 4 p.m.
Investigators were using a boat and a specially-trained dog to try and find any signs of Peterson.
The Illinois State Police was assisted on Monday by the FBI. Neither agency would speak officially about the operation -- except to say it was part of an ongoing criminal investigation.
Peterson's husband, Drew, is considered a suspect in her disappearance, but he has not been charged. Drew Peterson is behind bars; he was convicted of killing his third wife, Kathleen Savio, two months ago.