In which county is the UK prime minister's official country residence known as Chequers?

Chequers, or Chequers Court, is the country house retreat of the Prime Minister of the United Kingdom. The residence is located near Ellesborough, to the south of Aylesbury in Buckinghamshire, England, at the foot of the Chiltern Hills. Coombe Hill, once part of the estate, can be seen just behind. It has been the private retreat of the Prime Minister since 1921.