The incident happened in the sports ground of the Loreto Convent at around 6pm on Sunday.
The woman was walking her dog when she was approached a man who knocked her to the ground and sexually assaulted her before stealing some of her personal items.
The man was disturbed by two walkers and quickly fled the scene.
Gardaí arrived at the scene and the woman was taken to hospital for treatment.
A full technical exam of the scene was carried out while Gardaí carried out door to door inquiries in the area and gathered CCTV footage.
Garda Press have confirmed that a man in his 20s has been arrested in relation to the incident and is currently being held at Fermoy Garda Station
