Northumberland House was a large Jacobean townhouse in London, so-called because it was, for most of its history, the London residence of the Percy family, who were the Earls and later Dukes of Northumberland and one of England's richest and most prominent aristocratic dynasties for many centuries. It stood at the far western end of the Strand from around 1605 until it was demolished in 1874. In its later years it overlooked Trafalgar Square.

In British usage, the term townhouse originally referred to the opulent town or city residence of a member of the nobility or gentry, as opposed to their country seat, generally known as a country house or, colloquially, for the larger ones, stately home. The grandest of the London townhouses were stand-alone buildings, but many were terraced buildings.