(AP) -- Police in helicopters, with dogs and armed with rifles were conducting a massive manhunt in northern Illinois on Tuesday after an officer was fatally shot while pursuing a group of men.

An emotional Fox Lake Mayor Donny Schmit described the slain officer, Lt. Charles Joseph Gliniewicz, as a personal friend, a three-decade member of the department and a father of four sons.

"We lost a family member," Schmit said of the 52-year-old officer known around town as "GI Joe." ''His commitment to the people of this community has been unmatched and will be dearly missed."

Authorities said Gliniewicz radioed in to tell dispatchers he was chasing three men on foot in the village of Fox Lake, 55 miles north of Chicago. Communication with him was lost soon after, said Lake County Sheriff's Office spokesman Sgt. Christopher Covelli.

"His backup arrived shortly thereafter and found him injured with a gunshot wound," Covelli said. "The officer has succumbed to his injuries and passed away."

Undersheriff Raymond Rose told the Chicago Tribune that the officer had also been stripped of his gun and other equipment.

Less than an hour's drive from Chicago, the area is popular with boaters and for other outdoor pursuits because of its forest preserves and a chain of lakes that partly encircles Fox Lake. Some longtime city dwellers move to the region for what is normally a quieter lifestyle.

Police and other law enforcement officials, some of them in military-style camouflage, were seen taking up positions on rooftops and along railroad tracks, scanning the terrain with rifle scopes and binoculars. Others leaned out of helicopters with weapons at the ready.

Nearby Grant Community High School was placed on lockdown with children and staff instructed to say hidden and away from windows, and Schmit said that other schools were also put on lockdown, as staffers went from room to room to make sure the children were safe.

Authorities urged residents throughout the area to stay home while they conducted the search for three men, two of them white and the other black, using bloodhounds on the ground and helicopters above.

The service of a local commuter train was halted and residents who wanted to take their dogs out to relieve themselves were told to stay in their homes -- with the job of walking the dogs handled by police officers.

Gliniewicz's death is the third law enforcement fatality in Illinois this year, according to the Law Enforcement Officers Memorial Fund. It says firearms-related deaths in the U.S. are down 13 percent this year compared to the same period last year, Jan. 1. to Sept. 1; there were 30 last year and 26 this year.

Around Fox Lake, residents expressed their own sorrow over the death of the immensely popular Gliniewicz.

"This particular officer is a pillar in my community and definitely going to be missed, and (he) touched so many lives," said Gina Maria, a 40-year-old teacher who lives in the community.