Seaham is a seaside town in County Durham, England. Located on the Durham Coast, Seaham is situated 6 miles south of Sunderland and …Seaham is a seaside town in County Durham, England. Located on the Durham Coast, Seaham is situated 6 miles south of Sunderland and 13 miles east of Durham. The town grew from the late 19th century onwards as a result of investments in its harbour and coal mines. The town is twinned with the German town of Gerlingen.