Seaham, County Durham, also known as Seaham Harbour, is a port town on the north-east coast of England, located midway between the estuaries of the River Tyne and River Tees. The town was founded in 1828 by the 3rd Marquess of Londonderry, who wished to build a harbour for the export of coal from his mines in County Durham; the first coal was exported from Seaham in 1831. The new town was situated a mile south of the old village of Seaham. As well as being a centre for coal export, Seaham also had coal mines and glassworks, and was the centre of the Londonderry Railway, the largest privately-owned railway in Britain in the late 19th century, which served the Londonderry coal mines in east Durham. Seaham Hall in the old village belonged to the Milbanke family; here, in 1815, the poet Lord Byron married Anne Milbanke. It is now a spa hotel.
- The new town and port of Seaham Harbour was founded in 1828.