Camilla made a short speech in which she praised Club staff and participants, saying: "Here it is now, going from strength to strength. The only thing is, we now need an Ebony Horse Club in every major city!"
The 71-year-old Duchess has been the President of Ebony Horse Club since 2009.
The organisation, based in Brixton, south London, is a community riding centre which helps children learn new skills and responsibilities through care for horses.
The reception comes after a busy week for Camilla, who started the month with a five-day tour of Wales with Prince Charles to mark the 50th anniversary of his investiture as Prince of Wales.
On Saturday, the Duchess attended the private ceremony for Prince Harry and Meghan Markle's son Archie's christening at Windsor Castle, along with Prince William, Kate Middleton and Princess Diana's sisters Lady Jane Fellowes and Lady Sarah McCorquodale.
Just 25 people were invited to the intimate event, with Queen Elizabeth II and Prince Philip unable to attend due to prior commitments for the Queen in Scotland.