The town of Castleblayney is situated on the northern shore of Lough Muckno. Pre-historic sites in the area prove that the district was inhabited from the early times. In the late 7th Century the monastery was founded on the northern shore of the lake by St. Maeldoid.

It was not until Edward Blayney was granted the territory of Muckno in 1607 and built a Castle that a village began to grow. The growth of the town was very slow and not until the 18th Century that the modern town evolved. Andrew Thomas the 11th Lord Blayney was responsible for most of the work. The Market House was built at the end of the 18th Century, the Catholic Church was opened in 1814, the Church of Ireland in 1808 on the site of an older Church extended in 1829 when Lady Blayney presented stain glass windows. The Work House opened in 1842 and 81 paupers were admitted. By 1849 as a result of the Famine the numbers had reached almost 2000.

The linen trade and the coming of the Great Northern Railway all helped the town prosper and grow. Even after the slump in the linen trade the town was still evolving and expanding to the way it is today.

The 12th and last Lord Blayney sold his entire estate to the wealthy Henry Thomas Hope in 1853. Henry Hope improved the castle and beautified grounds. The name Hope still brings fame to the town not because of any deed that Henry did in the area but because of the ill-fated blue diamond which bears the name Hope Diamond.

The Castle was occupied by the Duke of Connaught son of Queen Victoria from 1900 - 1904. The Castle served as a temporary county hospital from 1932 - 1937.

The town of Castleblayney has survived and prospered. Despite the hardships of the emergency years of the Second World War and the slump in trade and business in the fifties when so many of the youth of the town were forced to emigrate. The population of the town has reached the 3000 mark and still expanding.