Windsor is a historic market town and unparished area in the Royal Borough of Windsor and Maidenhead in Berkshire, England. It is widely known as the site of Windsor Castle, one of the official residences of the British Royal Family. The castle is notable for its long association with the English and later British royal family, and for its architecture. The town is situated 21.8 miles (35.1 km) west of Charing Cross, central London, 5.8 miles (9.3 km) southeast of Maidenhead, and 15.5 miles (24.9 km) east-southeast of the county town of Reading. It is immediately south of the River Thames, which forms its boundary with Eton.