Port Glasgow, town (1991 pop. 22,636), Inverclyde, W Scotland, on the Firth of Clyde. Its dry dock, built in 1762, was one of the first of its kind in Scotland. It was founded in 1668 as a port for Glasgow, before the city had been made accessible to large ships. Port Glasgow became its own town in 1775. There are shipbuilding plants and textile, rope, and canvas factories. For a time, Port Glasgow held a leading place in Clyde sea traffic. The ruins of 16th-century Newark Castle are preserved among the Clydeside docks.