The royal couple spent their time mingling and chatting to guests, including representatives from charities, the Women’s Institute and people involved with children with special needs.
Also invited were business owners whose premises had been attacked in recent riots in Belfast, along with police officers injured during the disorder.
The duchess, who wore a summery lemon dress for the occasion, later joined her husband in a ceremonial tree planting in the castle grounds.
1. Royal garden party
The Duchess of Edinburgh chats with garden party guests at Hillsborough Castle. Photo: Jonathan Porter/PressEye
2. Royal garden party
Enjoying the garden party at Hillsborough Castle in the company of the Duke of Edinburgh, Prince Edward and his wife Sophie, the Duchess of Edinburgh. Photo: Jonathan Porter/PressEye
3. Royal garden party
Enjoying the garden party at Hillsborough Castle. Photo: Jonathan Porter/PressEye
4. Royal garden party
The Duke of Edinburgh, Prince Edward, meets business owners who recently had their businesses attacked during riots in Belfast. Photo: Jonathan Porter/PressEye