Halkin Street is named after Halkin Castle, Flintshire, a seat of the Grosvenor family, Dukes of Westminster, who own large swathes of Belgravia. The castle was designed by the architect John Buckler and built between 1824 and 1827 for Robert Grosvenor, who was at the time the 2nd Earl Grosvenor, and later the 1st Marquess of Westminster. The building of the castle was supervised by Benjamin Gummow, the Earl's architect and surveyor. It was used as a sporting lodge and, on occasions, for living accommodation. In 1886 the Chester firm of architects, Douglas and Fordham, added an extension in Elizabethan style for the 1st Duke of Westminster. The extension consisted of a wing containing a new drawing room. Internal alterations were made which included a staircase, and a chimneypiece in the dining room.