Cromstrijen (Cromstrien in local dialect) is a municipality on the Hoeksche Waard Island in the western Netherlands, in the province of South Holland. The municipality covers an area of 70.31 km² (27.15 mile²) of which 15.94 km² (6.15 mile²) is water. It was formed on January 1, 1984, when the municipalities on the Hoeksche Waard were realigned.
The municipality of Cromstrijen consists the communities Klaaswaal and Numansdorp (townhall).