Lough Rynn Castle was the seat of the Earls of Leitrim-the Clements family. Their association with Lough Rynn began in 1750 when Nathanial Clements bought 10,000 acres in the Mohill area. At that time the estate had no main house and was completely let to tenants, English and Irish. Nathanial, his son and grandson, who succeeded him were absentee landlords and never lived at Rynn. It was Robert Clements, the 2nd earls heir, who became the first Clements to reside at Lough Rynn and he brought the estate into the nineteenth century.
Robert in 1833, built a manor house overlooking Lough Rynn, which would become known as lough Rynn Castle, but in fact was a relatively modest, 2-storey house in a Tudor-revival style. He encouraged the most modern methods of farming among his tenants, However he did not live long enough to carry through most of his plans, as he died at the young age of 33.
The notorious Wm. Sydney Clements succeeded Robert,his brother, as the 3rd Earl of Leitrim. He took full ownership of the estate in 1854. Wm. Sydney is remembered mostly for callous and merciless acts against his tenants. He had a ‘hasty imperious temper’ which got worse over the years.
At the beginning, however, he continued the work his brother had started and was thought to be a good and just man. He threw himself into the task of making Lough Rynn a model estate. He added more out-buildings, including a coach house, stables, dairy and stores. He had a flair for Architecture and had many of his own designs built by stonemasons brought in from London. Sydney also undertook major land reclamation and outlawed many of the old wasteful farming methods on his estate. He planted a range of trees throughout his estate, including many unusual ones imported from abroad. He also created tree-lined walks and pleasure gardens around his house. Many of these superb trees survive in the castle grounds to this day.