Gosford Castle is situated in Gosford, a townland of Markethill, County Armagh, Northern Ireland, close to the border with County Down. Construction of the castle began in 1819 and finished in the 1850s. It was commissioned by Archibald Acheson, 2nd Earl of Gosford and the architect was Thomas Hopper, one of the leading London architects of the first half of the 19th century. It is the largest Grade A listed building in Northern Ireland.