Althorp has been the family home of the Spencer family for nearly 500 years. In 1508 Sir John Spencer bought the Althorp estate and built the first house there around the same time. It was a red-brick structure surrounded by a moat (filled in during the 1790s). Althorp was substantially altered in 1650 by the 1st Earl of Sunderland’s Countess, Lady Dorothy Sydney, who converted the Tudor inner courtyard to a vast drawing room and added the main staircase. The present building, however, is mostly late 18th-century work by Henry Holland. The 9th and present Earl has expressed his regret at this transformation of Tudor and Stuart gem but admits that it made maintenance much easier over the next 200 years. Nevertheless the entrance hall in Palladian style, together with its fine plaster ceiling, survives from the 1730s, over half a century earlier. The design was by Roger Morris, who is also responsible for the stable block, and Colen Campbell. Known as the Wootton Hall after the massive painting on the walls by John Wootton (1678–1765), it was considered by Sir Nikolaus Pevsner to be the noblest Georgian room in Britain. The former art collection, once among the most splendid in private hands anywhere, has suffered considerable depredations in recent years.

Althorp has in recent years become globally recognised as the final resting place of Diana, Princess of Wales. Visitors are welcomed to Althorp to view the house, grounds and the acclaimed exhibition celebrating the life of Diana, housed in the converted 18th-century stable block. Visitors to Althorp help to continue the work of Princess Diana, as all profits raised are given to charity. So far visitors have generated over $1m.