Longstone is a hamlet in Cornwall, England, UK. It is part of the civil parish of St Mabyn, and is about one mile east of St Mabyn village on the B3266 road. It is named after the menhir which formerly stood here.
The "Longstone" was a standing stone which was broken up for gateposts around 1850. It was said to have been inscribed, thus making it early medieval.
There is however a later medieval cross by the crossroads. It consists of a medieval crosshead placed on a modern rough hewn shaft which has been set into a medieval slab base.
Coordinates: 50°31′41″N 4°44′14″W / 50.5281°N 4.7371°W