PIP police got the initial call around 8:30 p.m., Police Chief Michael Coppola said Wednesday.
Marine units and patrol officers responded, he said.
"While searching for the individuals it was learned that they were part of [Camp Rominu in Monticello] for mentally and physically challenged children," Coppola said.
The 15 children and six adults -- ranging in age from 15 to 33 -- "were separated into several groups over a two-mile distance," the chief said.
"Limited cooperation from counselors added to the delay," he added.
The marine units removed several people from several locations "over the course of several hours along the Shore Trail," Coppola said.
All were brought to the Alpine Boat Basin.
By 3 a.m., "all members of the group were accounted for," the chief said.
"A camp transport van met the group and transported them back to their place of origin," he said.
No injuries were immediately reported.
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