Over the weekend, they could be seen digging up a 100 square foot area on remote private farmland near Peoria, reports CBS News Correspondent Cynthia Bowers.
"They're conducting a very meticulous, methodical search of the area. I'm in the position to say now that we are digging," Master Sgt. Tom Burek, of the llinois State Police, told reporters.
Police have said they're acting on a tip, but deny reports it was a jailhouse tip.
Stacy's husband, Drew Peterson, now 56, a former Bolingbrook, Ill. police sergeant, remains the only suspect in her October2007 disappearance, but has never been charged and denies wrongdoing.
She was his fourth wife, and the couple had two children together.
In a September 2008 "Early Show" interview, Drew Peterson claimed Stacy had run away.
Co-anchor Maggie Rodriguez asked, "Do you feel that she's out there with another man, hasn't called anyone, left her children behind, dropped off the face of the planet and no one's even seen her?"
And Peterson replied, "I believe that 100 percent, without a doubt."
Following Stacy Peterson's disappearance, authorities took a new look at the mysterious 2004 drowning death of Peterson's third wife, Kathleen Savio. After prosecutors exhumed her body, the death was ruled a homicide. Peterson was arrested and charged with her murder in May of last year.
His lawyers say the latest search is just a ploy to drum up attention in advance of his July trial. "The one thing all the rumors have in common is that they proved to be false, every single one of them," Joel Brodsky remarked to CBS News.
Jury selection in Peterson's trial is scheduled to being on July 8.