The site at Templepatrick was supposedly once held by a thirteenth-century fortified priory of the Knights of St John. The evidence for that is thin enough that some historians doubt the priory ever existed. What is certain is that Sir Robert Norton - an officer under Sir Arthur Chichester, the Plantation Governor of Carrickfergus - obtained lands along the Six Mile Water in the late sixteenth century and began building what is now the east wing of the castle around 1610. The Norton family came to Ulster as part of the Plantation, the seventeenth-century scheme that resettled Protestant Scots and English on lands cleared of Gaelic Irish chieftains. The Upton family bought Norton's house soon after, and the Uptons - who became Viscounts Templetown in 1776 - kept it for nearly three hundred years.

In 1776, Clotworthy Upton was created Baron Templetown after serving in the household of Princess Augusta, the dowager Princess of Wales. He commissioned Robert Adam to remodel his Antrim seat in the castellated Gothic style then fashionable. Adam's plans, sent from Britain, altered the roofline, added a new north wing with battlements, and produced a domed mausoleum that was completed beside the castle in 1789. The stable block - the double courtyard now known as Adam Yard - copied the exact architectural details of the old Fish Market of Leith, near Edinburgh, which has since been demolished. Castle Upton thus preserves, in stone, a Scottish building that no longer exists in Scotland. Adam's successor at Castle Upton, the Second Viscount, hired Edward Blore in 1837 to remodel the house again. Some Adam work survived. The mausoleum has lasted entirely.

The Templepatrick Old Burial Ground beside the castle holds the Templetown Mausoleum and, remarkably, the grave of William Orr - the United Irishman whose 1797 execution in Carrickfergus became one of the rallying cries of the 1798 rebellion. Remember Orr, the rebels shouted at the Battle of Antrim. He is buried in the same churchyard as the Ascendancy family whose mausoleum towers nearby - the political opposites lying within yards of each other. The graveyard also holds Josias Welsh, a Geneva-educated Presbyterian preacher who was a grandson of John Knox, the leader of the Scottish Reformation. Three currents of Ulster history - the Anglo-Irish Protestant Ascendancy, the radical United Irishmen, and the Scots Presbyterian dissenting tradition - share a single small acre of ground.

Castle Upton fell into poor repair in the early twentieth century. Sir Robin Kinahan and his wife Coralie de Burgh bought it in 1963 and began the long restoration. Adam Yard, the stable block, was converted into housing. The castle itself was eventually opened as a wedding venue by their son Danny Kinahan, the Ulster Unionist MP, and his wife Anna. The Italian marble chimney now warming the ballroom in the Adam wing was salvaged from Downhill Castle in County Londonderry. In 2016 the Kinahans put the property on the market for £1.35 million. The mausoleum, a National Trust property, remains open to the public - George Upton, 3rd Viscount Templetown, Crimean War veteran and Gold Stick in Waiting to Queen Victoria, lies in it. Around them, the Six Mile Water still flows past stones that have stood through Plantation, rebellion, and centuries of Antrim weather.