The land beneath Castlebellingham has been worked for a very long time. Around the village and the neighbouring townlands of Greenmount and Kilsaran, archaeologists have found fulachta fiadh - the cooking pits of Bronze Age Ireland - along with ring ditches and a motte and bailey that marks the arrival of the Anglo-Normans. From at least 1301 the place was called Gernonstown, after a Norman family whose name had a quietly comic origin: gernon, an old French word for moustache. Some forgotten Norman ancestor had a notable enough one that the nickname stuck. A religious house at Kilsaran, rumoured in old records to have had Templar connections, has long since vanished without trace. The Gernons themselves faded too. What stayed was the land.

Henry Bellingham came to Ireland during the English Civil War as a cavalry officer. He was good at his work, and when Cromwell finished reorganising Ireland in the 1650s, Henry was given the lands of Gernonstown - native Irish estates redistributed to English soldiers in lieu of pay. The Acts of Settlement and Explanation confirmed his title, and in 1666 Charles II formally granted the lands to him for his "faithful service as a good soldier in the late wars." Henry's family had come from Kendal in Westmorland, far away in northwest England, but they made Louth their home. The first Castle Bellingham did not last long. Jacobite forces destroyed it during the Williamite War in Ireland, the conflict that climaxed at the Boyne in 1690. Thomas Bellingham rebuilt it in the 1690s, and it is that house, much altered, that stands today.

Sir Alan Henry Bellingham, the 4th Baronet, lived from 1846 to 1921 and shaped the village more than any of his predecessors. After his first wife Lady Constance died young, he raised the roadside Calvary near the castle in her memory - a Catholic devotional shrine standing in a county that still bristled with the politics of religion. He filled the upper walls of village buildings with inset religious panels and had biblical verses cut into window sills. North of the castle he built a tidy row of "widows' dwellings," almshouses for women left alone, paid for from his own pocket. After the First World War a Celtic-style war memorial rose in 1920, unveiled by Cardinal Logue, Primate of All Ireland. The Bellinghams stayed until the late 1950s. The last of them at Castlebellingham was Brigadier General Sir Edward, born 1879, who served as the last Lord Lieutenant of Louth in 1921 before the Irish Free State swept the office away.

Castlebellingham railway station opened on 1 April 1851 and closed for good on 6 September 1976. The village had been a coaching stop on the Dublin-Belfast road for centuries, and the rumble of through-traffic was part of its character into the late 20th century. That changed in early 2001 when the M1 motorway opened a Dunleer-to-Dundalk section that lifted the heavy traffic off the village street. In September 2010 a motorway service area was built at Castlebellingham, putting the village's name back on the highway signs even as the village itself stayed quiet. The castle today is a hotel. The widows' dwellings still stand. The carved verses on the window sills are weathered but readable - a 19th-century baronet's faith, preserved in stone, walking distance from the M1 services.