USD Castelsardo (Unione Sportiva Dilettantistica Castelsardo) is an Italian association football club based in the municipality of Castelsardo, Sardinia. Founded in 1967, the club operates as an amateur sporting union, participating primarily in the regional divisions of the Italian football league system.
The club's official colors are red and blue, and it plays its home matches at the Stadio Comunale di Castelsardo. Throughout its history, the team has predominantly competed in the regional Sardinian tiers, including the Eccellenza and Promozione divisions. At various points in its history, most notably during the late 20th and early 21st centuries, the club achieved promotion to Serie D, the highest level of non-professional football in Italy.
As a representative of a town in the Province of Sassari, USD Castelsardo serves as a local institution for athletic development and competitive sports in the northern region of Sardinia. The organization is governed by the regulations of the Italian Football Federation (FIGC) through the regional committee of Sardinia. Precise details regarding current league standings and squad compositions vary by season and are managed within the framework of Italian amateur sports registries.