Walter Long of Preshaw House, Hampshire, JP, DL (24 November 1788 – 5 January 1871) was an English landowner.
On the death of his father in 1797 he inherited the estate of Preshaw at Upham with its Elizabethan mansion, surrounded by approximately 1,670 acres (6.8 km2), and in 1810 commissioned John Nash to make alterations to the house.
Prior to ownership by the Trenchards (from 1617), Overcourt had been owned by Henry Long, Lord of the manor of Southwick, and was at one time a royal hunting lodge.
The present building dates from the late 14th century, and was restored by Edward IV for his mother Cecily, Duchess of York.
Walter Long also inherited the estates in Somerset and Dorset on the death of his uncle, the eminent surgeon of St Bartholomew's Hospital, William Long of Marwell Hall, in 1818, and those in Oxfordshire on the death of his cousin John Blackall in 1829, which included Haseley Court.