Trewen parish is bounded to the north by Egloskerry parish, to the east by St. Thomas-by-Launceston Rural, to the south by South Petherwin and to the west by Altarnun and Laneast parishes. The population of Trewen parish in the 2001 census was 134.
The hamlet of Trewen is situated 5 miles (8 km) west of Launceston. The little parish church of St Michael has a bellcote rather than a tower. The only other hamlet in the parish of Trewen is Piper's Pool which straddles the A395 road.
Trewen was part of the Launceston Rural District from 1894 until 1974.
One of the many maps available on A Vision of Britain through Time is one from the Ordnance Survey Series of 1900 illustrating the parish boundaries of Cornwall at the turn of the 20th century. This map blows up to show all the parishes and many of the small villages and hamlets.
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