Westvoorne is a former municipality on the island of Voorne-Putten in the western Netherlands, in the province of South Holland. The former municipality covered an area of 97.48 km2 (37.64 sq mi) of which 44.30 km2 (17.10 sq mi) was water. It had a population of 14,900 in 2021.

Brielle, also called Den Briel in Dutch and Brill in English, is a town and historic seaport in the western Netherlands, in the province of South Holland, on the north side of the island of Voorne-Putten, at the mouth of the New Maas. The former municipality covered an area of 31.14 km2 (12.02 sq mi) of which 3.59 km2 (1.39 sq mi) was water. In 2021 its population was 17,439.