Rockhill House is older than the Irish state by three centuries. Captain Thomas Chambers is the earliest recorded occupier, in 1660. The present 30-room stone building dates from 1824 and is a protected structure. For most of its history it was a country house of the gentry, set on 29 acres of land just south of Letterkenny. During the Irish Civil War of 1922-23, anti-Treaty Republicans - the Irregulars - occupied the house and were removed by a pro-Treaty crowd led by a local man named James McMonagle. Later in the 1920s and 1930s the house belonged to Sir Charles John Stewart, who lost both his sons in the First World War and eventually sold the estate in October 1936, citing fear of IRA attacks. The Free State took it over. During the long vacancy that followed it served briefly as a Preparatory Irish College. In 1969 the Irish Army moved in.

The reason for the army's arrival was sixty miles up the road. In August 1969, riots in Derry and Belfast had escalated and Northern Ireland was slipping into what would become the Troubles. Taoiseach Jack Lynch responded with a televised address - "the Irish Government can no longer stand by" - and ordered the army to set up field hospitals along the border to receive nationalist refugees fleeing the North. Rockhill, just outside Letterkenny, was an obvious location: within easy reach of the border crossings at Lifford, Strabane, and Derry. The 24th Battalion garrisoned it from 1969 to 1973. The 28th Infantry's B Company took over thereafter and held the post for thirty-six years. Throughout the worst years of the Troubles, Irish soldiers based at Rockhill patrolled the southern side of the border, intercepted arms shipments, and assisted in the search for victims when bombs went off on either side.

Long before the army arrived, Rockhill's lawns hosted a different kind of activity. A surviving letter from a Stewart estate steward, written before 1900, reports to his absent master that golf is being played on the grounds: "Mr Chambers, Manager of the Ulster Bank, Dr Carre and a few others been playing golf on the lawn, starting at McDaid's old lodge and going across into the Fort Field." The Letterkenny Golf Club was not formally established until 1913. The Stewart steward's letter is the earliest documented evidence of the game being played in this corner of Donegal. It is the kind of detail that makes the Rockhill story particular - the same field that gentlemen of the Ulster Bank crossed with mashie irons before the First World War later carried the boots of Irish soldiers patrolling against a different war eighty years later.

The closure of Rockhill in the 2008 budget cuts was politically explosive in Donegal. Minister for Defence Willie O'Dea defended the decision: "There were too many army barracks for an army and a country of Ireland's size." Local people calculated that the closure would cost the local economy €6.5 million annually and remove the only army presence from the entire north of County Donegal. The most theatrical moment came in the Dáil, when Donegal TD Dinny McGinley, frustrated by O'Dea's refusal to come to the county and explain the decision, demanded to know whether the minister was "a man or a mouse." The Leas Ceann Comhairle, Brendan Howlin, asked McGinley to leave the chamber when he kept shouting. The barracks closed anyway. An open day was held on 14 January 2009. A final mass was celebrated by army chaplain Father Alan Ward on 18 January. The soldiers marched out ten days later.

In the years since closure, Rockhill House has not found a clear future. Lieutenant-Colonel Declan O'Carroll, a former commanding officer, suggested it could house the County Museum, which is short of space at its current location. A former Green Party politician proposed converting it into a boot camp for young offenders. The Rockhill House Heritage Association has campaigned since 2009 for the estate to be developed as a flagship tourism project. In August 2014 the property went to public auction and was bought by a local businessman, John Moloy, for €670,000 - a remarkably modest figure for a 30-room listed building on 29 acres. As of 2026, the house is privately owned but largely empty. The barracks buildings, the parade grounds, the avenue down which the soldiers made their last march - they wait.