The first written mention of Úsov is from 1260. The castle was built around 1250. Before 1487 the lords of Vlašim modified the castle. In the 16th century, Úsov was in the possession of the lords of Boskovice, an in 1597 it was acquired by the House of Liechtenstein. The Liechtensteins owned the castle until 1945.
The castle was damaged during the Swedish occupation in 1643. During the rule by Hans-Adam I of Liechtenstein, in 1692–1699, it was reconstructed and partially rebuilt into a large three-storey Baroque residence, designed by Domenico Martinelli.
Towering 52 meters above the sea, Bengtskär lighthouse is the tallest one in Scandinavia. The building started in in 1905 after the shipwreck of S/S Helsingfors and was completed in 1906. The lighthouse was designed by architect Florentin Granholm. On December a special petrol lantern, designed and built in Paris, was brought to Bengtskär and installed atop the tower.
German fleet bombarded Bengstkär in the First World War in 1914. Since the Gulf of Finland was heavily mined, it was not until 1919 that the surrounding seas were declared safe for shipping, that the light was lit again.
After the war the military value of Bengtskär increased as part of the defence system of independent Finland. In Second World War (1941) Soviet Union made a suprise attack to island. After a bloody battle, the small Finnish garrison emerged victorious. Intermittent repairs to the facility continued during the post-war period.