The toponym comes from Old English, either Thures mere ("Thur's pool") or Þyrsmere ("a lake haunted by a giant or demon").

[3] The Domesday Book records that in 1086 the manor of Tusmore belonged to Walter Giffard, 1st Earl of Buckingham.

In 1828 the last William Fermor died without a male heir and left the estate to his adopted daughter and her husband, John and Maria Turner Ramsay.

In 1929 the heir of Henry Alexander Gordon Howard, 4th Earl of Effingham sold the estate to Vivian Smith, a merchant banker who in 1938 was created 1st Baron Bicester of Tusmore.

It seems to have ceased to exist by the early part of the 16th century, as records of episcopal visitations at that time make no mention of Tusmore.

Mylne laid out the gardens and landscaped the park, the latter with a lake and an ornamental Temple of Peace dedicated to the late poet Alexander Pope (1688–1744).

[4] Smith greatly changed the gardens and park, retaining little of Milne's landscape design except the Temple of Peace and the lake.

[6] In 2004 the Georgian Group gave the completed house its award for the "best new building in the Classical tradition",[7] although doctrinaire modernist architectural critics have been sceptical.

[8] Outbuildings, lodges and a monumental obelisk to commemorate the Millennium have been completed for Wafic Saïd, all to the design of Whitfield Lockwood.

As part of extensive landscape works the patte d'oie has been reinstated and a wide double avenue from the entrance to the house and terminating at the obelisk established.

On 2 September 1941 a Junkers Ju 88 fighter-bomber of Luftwaffe Nachtjagdgeschwader 2, flown by flying ace Oblt Paul Semrau, bombed RAF Upper Heyford.

He and two other crew are buried in the Commonwealth War Graves Commission section of St Mary's parish churchyard, Upper Heyford.