Princeton, where HMP Dartmoor was built, lies within the parish of Lydford.
From White's Devonshire Directory, 1850:
"LIDFORD, or Lydford, is a small ancient village, on the banks of the small river Lyd, and on the western side of Dartmoor, 7½ miles N. by E. of Tavistock. Its parish contains 280 souls, and 3064 acres of land, exclusive of DARTMOOR FOREST QUARTER, which has a scattered population of 933 souls, and extends over about 53,900 acres of wild moorland hills and dales, including the hamlets of Prince Town, Hexworthy, Huckaby, Dinnabridge, Two Bridges, and the extensive but now unoccupied Prison of War."