​SEAHAM HARBOUR, a seaport and urban district, in the South-eastern parliamentary division of Durham, England, 6 m. S. of Sunderland by a branch of the North-Eastern railway. Pop. (1901) 10,163. The harbour was built (1828) by the third marquis of Londonderry to facilitate the export of coal from the mines on his adjacent property. Besides the coal trade there are extensive bottle and chemical works.