The first Agricultural Show in the Demesne was held on 22nd August 1928. The show secretaries were Mr J.G. Jamison, Miss Ryan and Mrs P.D.Savage.
There were classes for horses, cattle, swine, sheep, goats, poultry, butter and eggs, grazing fields, baking, embroidery and crochet, art, handicrafts, children's flowers, horse jumping and sheep dog trials. It ran until 1939 until World War II started.
In 1967 a new seven man committee in partnership with the Ulster Riding and Jumping Club organised the first Horse Show in Castlewellan since 1939. The date was that used by URJC ie. the first Saturday after the 12th July holidays. It took place in Castlewellan Estate which had recently been purchased by the Forestry Service from Mr. Gerald F. Annesley.
This partnership continued until 1982 when the two committees agreed to go their separate ways, and the show was organised solely by the Castlewellan Show committee. Violet Bell, became Show Secretary in 1984 and was a tireless presence up until her retirement in 2012 after 28 years at the helm.
While equine classes continued to be an important element of Show day, the numbers entering cattle, goats and sheep grew and today it hosts the largest one day sheep competition in Northern Ireland. Poultry classes were introduced by Pauline Gibson in 2009 and have proved very popular.
In 2013 Castlewellan Show featured on the BBC tv programme Farm Fixer with Nick Hewer, whose advice certainly focused the minds of the committee. Social media has become an important way to promote the Show as well as profile the animals and the people. The Show has a website, a facebook page and a twitter account.
Over the years, there has been an increase in trade stands, food and craft producers and more focused family entertainment with over 300 classes and 2000 entries from local schools. The primary reason for the Show is to showcase rural life and there has been a steady increase in visitors from all over the world.