Fort Willem II of Ungaran is a late 18th-century fort built by the Dutch in Ungaran, Semarang Regency, Central Java, Indonesia. Its main purpose was to control an important trade route between Semarang and Yogyakarta. The fort is the place where Prince Diponegoro was imprisoned while waiting for his judgment in Batavia and further exile to Makassar. The fort is currently used as a dormitory for the families of Indonesian police personnel.