Ashdown House is a 17th-century country house in the civil parish of Ashbury in the English county of Oxfordshire. Until 1974 the house was in the county of Berkshire, and the nearby village of Lambourn remains in that county.

Ashbury is a village and large civil parish at the upper end (west) of the Vale of White Horse. It was part of Berkshire until the 1974 boundary changes transferred it to Oxfordshire. The village is centred 7 miles (11 km) east of Swindon in neighbouring Wiltshire. The parish includes the hamlets of Idstone and Kingstone Winslow. The 2011 Census recorded the parish's population as 506.