Newcastle is a village in Monmouthshire, Wales.
It is situated within the NP25 postcode district, which is within the Monmouth post town.
NP25 is the only postcode district within the Monmouth post town.
The Monmouth post town is within the Newport postcode area.
Administrative Ward: Llantilio Crossenny
Administrative District: Monmouthshire
Country: Wales
UK Parliament: Monmouth