Castellammare del Golfo is a town and municipality in the Trapani Province of Sicily. The name can be translated as "Sea Fortress on the Gulf", stemming from the medieval fortress in the harbor. The nearby body of water conversely takes its name from the town, and is known as Gulf of Castellammare.

The province of Trapani is a province in the autonomous island region of Sicily, Italy. Following the suppression of the Sicilian provinces, it was replaced in 2015 by the free municipal consortium of Trapani. Its capital is the city of Trapani. It has an area of 2,469.62 square kilometres (953.53 sq mi) and a total population of 433,826 (2017). There are 25 comuni in the province.