Hellevoetsluis is a small city in the western Netherlands. It is located in Voorne-Putten, South Holland. The former municipality covered an area of 61.20 km2 (23.63 sq mi) of which 20.10 km2 (7.76 sq mi) was water and it included the population centres of Nieuw-Helvoet, Nieuwenhoorn, and Oude en Nieuwe Struiten, all former municipalities.

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.