Police made the discovery at about 1pm in a field off Robin Hood Copse, between Castle Hill and Eversley Road.
Officers had been conducting a search in connection with a missing person inquiry.
Senior investigating officer, Detective Chief Inspector Gill Wootton said: "We have launched an investigation following the discovery of a woman's body.
"This investigation is in its very early stages and we will now be carrying out extensive enquiries.
"The woman has not been formally identified, but the family of the missing woman are being kept fully updated on developments in this inquiry.
"A cordon has been put in place around where the body was found so we can carry out a thorough examination of the scene."
The death is being treated as unexplained.