Westmaas is a village in the Dutch province of South Holland. It is located about 14 km south of the city of Rotterdam, next to Mijnsheerenland in the municipality of Hoeksche Waard. In 2020, the population was 2,065. Westmaas developed after the Munnikenland was enclosed by a dike in 1439. The village was founded by Carthusian monks. It became an independent parish in 1458. The Dutch Reformed church is an aisleless church built in 1651. It was restored between 1966 and 1967.