Castletown is a village in Dorset, England.
It is situated within the DT5 postcode district, which is within the Portland post town.
DT5 is the only postcode district within the Portland post town.
The Portland post town is within the Dorchester postcode area.
Administrative Ward: Underhill
Administrative District: Weymouth and Portland
Administrative County: Dorset
Country: England
UK Parliament: South Dorset
NHS Local Health Authority: South West
NHS Region: Southern