UPDATED 
No one knew where it was until an Englishman decided to return it.

DID THEY EVEN KNOW IT WAS MISSING

Missing part of Stonehenge returned, 60 years on

A nonagenarian retiree from Florida returned a piece of Stonehenge -- missing for six decades -- to caretakers of the monument, British officials said Wednesday.

Florida man returns piece of Stonehenge 60 years after restoration work

A nonagenarian retiree from Florida returned a piece of Stonehenge -- missing for six decades -- to caretakers of the monument, British officials said Wednesday.

ABC.NET.AU

Missing piece of Stonehenge returned after 60 years abroad, may help reveal origins of monoliths

A missing piece of Stonehenge has been returned 60 years after it was taken, English Heritage which looks after the prehistoric site has revealed.