Part of the Hesketh Estate near Towcester in Northants has been sold.
Easton Neston house is more than 300 years old
The former Tory party treasurer Lord Hesketh put the 16th century Easton Neston estate on the market last year for £50m, but there were no buyers.
The estate was divided up and a private buyer has bought houses in Hulcote, the Grade II listed Pomfret Lodge and 2,000 acres of land for an undisclosed sum.
On Monday, estate agent Knight Frank described the deal as "the most important land sale of the year".
Easton Neston House remains on the market for about £18m, along with the remaining houses in Hulcote.
The family has decided to keep Towcester racecourse.
On Tuesday, Sotheby's are auctioning part of the collection of works of art and furniture from Easton Neston house, which is expected to fetch more than £5m.
The Grade I listed stately home, set in more than 3,300 acres, has been the family seat of the Fermor-Hesketh family for 470 years.
With annual losses at Easton Neston estimated at more than £1m a year, Lord Hesketh felt he had to sell to safeguard his family's financial future.