Sorn is a Celtic word, meaning a promontory, or rising-ground of frowning aspect. Sorn Castle undoubtedly received its name from its situation, as it stands high on a precipitous rock overhanging the water of Ayr. Almost sheer down from its massive walls, forty or fifty feet below their foundations, the clear stream dashes and tumbles over its rocky bed. At the time when the castle was built a site was eligible only as it showed advantages for purposes of defence. In such days the situation must have seemed an ideal one. From the side facing the river, the castle was almost impregnable, and the undulating country which stretched beyond could easily be overlooked from the castle walls. In front, the bare, treeless expanse of those days would offer no hiding place from watchful sentries. Such a stormy, troublous epoch has, happily, long since passed away, and the castle has again and again been adapted to meet the wants of the times, but in all its changes it has ever been the effort of its restorers to conserve its strictly Scottish style of architecture. In that they have been successful, and it is now a stately pile, with turreted windows, or low, broad casements, the crest of the Somervell family carved in high relief beside the entrance hall, the new part and the old blending into each other without the slightest incongruity. Its situation, chosen at first undoubtedly for defence, is now considered admirable because of its beauty. At an elbow-like turn in the river, near the kirk of Sorn, the bank on one side rises from almost canal-like flatness to steep bluffs and perpendicular scars of rock.  And high on its rocky promontory above the clear, impetuous stream, where its waters are caught and deepened and silenced in a long, slanting weir, stands this castle of Sorn. Of reddish stone, with windows set far back, like eyes deep-sunk with age, it is outlined through intervening trees or seen above their swaying branches.

The lands of Sorn belonged originally to the Keiths of Galston. Janet de Keith, heiress of Galston, married, first, Sir David de Hamyltoune of Cadzow, ancestor of the ducal house of Hamilton, and, secondly, Sir Alexander Stewart of Darneley. To her son of the first marriage, Andrew de Hamyltoune, she granted the lands of Sorn among others, and the charter was confirmed under the great seal on the 11th December, 1406. Whether the castle was built before that time or no does not appear, but the likelihood is that its erection was of an earlier date. Its first form was that of a keep, and there is a tradition to the effect that the masons employed in building it had the option for their wages of l.5 d per day or a peck of meal. If not built before Andrew de Hamyltoune's time, it must have been built when he acquired the land, for it became his residence.

The proprietors of Sorn Castle and descendants of Andrew de Hamyltoune have been among the most illustrious families in the kingdom.  Andrew Hamilton married Agnes, a daughter of Sir Hugh Campbell of Loudoun, Sheriff of Ayr, and by her had a son, Sir Robert Hamilton of Sorn and Sanquhar. Sir Robert married a daughter of Sir William Crawford of Lorhnorris; and Sir William Hamilton of Sorn and Sanquhar, a son of this marriage, was one of the Senators of the College of Justice and Lord Treasurer to King James V, as well as Captain of Edinburgh Castle.  He married a Kennedy daughter of the family of Cassilis, by whom he had an heiress, Isobel Hamilton, who married George, 7th Lord Seton.

James V visited Sorn Castle by invitation of George, 6th Lord Seton on the occasion of his son's marriage to the heiress Lady Isobel Hamilton, and which marriage brought Sorn to that family.  The chair which His Majesty is said to have used on the occasion was kept in Sorn Castle till the sale of the estate in 1782, when it was transferred to Loudoun Castle, where it still remains. It is a large chair of oak, of curious workmanship, with the arms of Sir William Hamilton carved upon the back.

The story of the King as he travelled to Sorn is: 

Yet the marriage of the Isobel was a very important one also, and Sir Richard Maitland in his "Historie of the House of Setoune," says that "the union was devised to bring about an alliance betwixt the Setounes and the Governor Arran, to whose house Sir William belonged, and was of such political importance that a medal commemorating it was struck, bearing the initials of the bride and bridegroom, I. H. and G. S., and the motto, "ung loy, ung foy, ung roy," is of great historical interest, as an example of ancient phonetic spelling of French!

George 7th Lord Seton and Isobel Hamilton were parents to Robert, 8th Lord Seton who became a great favourite of James VI and was created by him 1st Earl of Winton, by a charter dated 16th Nov 1600; to Alexander, 1st Earl of Dunfermline and Chancellor of Scotland under James VI; to Sir John of Barnes; to Sir William of Kyllismuir, and to Margaret who's marriage was celebrated at Lord Seton's castle of Niddry to Claud Hamilton, Lord Paisley, ancestor to the Earl of Abercorn.

The lands and castle of Sorn were sold by the succeeding Robert Seton, 2nd Earl of Winton to the family of Loudoun, and after remaining in that family for upwards of a hundred and fifty years they were sold to William Tennent, Esq., of Poole, in 1782."

The troop of dragoons quartered at Sorn killed at least two lads in high-handed fashion, one at Tinkhornhill, and another, at the instigation of the curate of Sorn, at Tarbolton; many a conventicle was scattered at their approach, and the moors and moss hags in the neighbouring parish of Muirkirk are dotted with memorials of martyrs of the Covenant. What tyranny they exercised over the poor people we can well imagine. Their power was unlimited, and they were not the men, as those murders testify, to fall short in its use. The prayer which heads the written oath "God save the King " was the watchword of the day.

About the beginning of the eighteenth century, Hugh, first Earl of Loudoun, married a daughter of John, first Earl of Stair. The lands of Sorn belonged to the Earl of Loudoun, and in the year 1727 the Countess took up her residence at Sorn Castle. She came to Sorn as the Dowager-Countess, and lived there for the long period of fifty years. When she died she was within a few months of completing her hundredth year. In those days servants clung to the service of one family, and seemed almost as much a part of the household as the sons and daughters. Most of the servants that the Countess brought with her remained during her life in her service, and some of them attained nearly as great an age as their mistress.

When the Countess of Loudoun came to Sorn, instead of the beautiful grounds laid out in the highest style of art which now surround the castle, and the lovely winding walks, shadowed by great trees along the banks of the Ayr, and a highly-cultivated tract of country stretching on every side with hedges and trees and plantations, the Countess found a bare, dreary expanse, with not a single road or hedge and very few trees. The castle was built around a courtyard at that time, and had all the characteristics of a fortress or keep. Her chronicler quaintly says that the Countess was not discouraged although she came from "a better country." She immediately set about working a great reformation in her surroundings.

She found only a very small garden and orchard; those she enlarged considerably and improved. She took an extensive farm into her own hands, enclosed the fields in hedges and interspersed them with belts and clumps of planting. She also adorned the banks of the river with trees and walks and the banks also of tributary rivulets. Scenes of beauty sprang up around her, to her great enjoyment. Many of the trees were planted and pruned by her own hands, and some of them remain to this day-giants of the woodland. The reformation the Countess initiated in agricultural matters was gradually followed by neighbouring proprietors. Mr. Steel, Mr. Farquhar of Gilmilnscroft, and Mr. Dunlop of Garnkirk took up the matter enthusiastically and the centre of the parish soon displayed a wonderful improvement.

Mr. Tennent, the next proprietor, repaired the castle in a most thorough manner and built large additions to it. Among the additions was a most magnificent drawing-room, and a very handsome staircase. The castle was described by a writer of the time as a most spacious, commodious, and comfortable mansion.

In the year 1837, while a walk was being formed along the side of the Cleugh, some workmen came upon a wonderful treasure-trove. It was no less than five hundred coins of copper and silver, some of them dating so far back as the fourteenth century-the reign of Robert III. There were also representative coins of the reign of each James. It was supposed that they had been hidden by the Covenanters in the days of the Persecution. Perhaps the exact spot where they were hidden was forgotten, and some expectant soul may have toiled and dug many places in vain for his hidden treasure, or death may have come suddenly and snatched away their owner without giving him time to confide the secret of the hiding-place to another.

They may have been stolen and hidden there, but it seems more likely that it was a treasure hidden for safety. The denomination of the coins is pathetically small, even for the great value of money of the times, like a long, well gathered hoard. The silver coins are very little- some of them round, others octagonal, with edges as if clipped. Such a find naturally was noised abroad, and although the workmen delivered the coins to Mr. Somervell, he was not allowed to keep them. The Government claimed them, and they were sent off. About fifty were returned from the Exchequer, and are kept as antiquarian curiosities in the castle.

The last time that the castle was repaired or restored was upwards of thirty years ago, when Mr. Somervell again added to it and very considerably improved it. It is of the pure Scottish type of architecture, and has not suffered from the many heads and hands that have planned and worked at it, for it has been the endeavour of each succeeding restorer to retain its characteristic style. It is a handsome building in every way, and a commodious and beautiful residence. In the Island of Westray there is a ruined castle of massive Scottish architecture to which the castle of Sorn bears a striking resemblance. But while the castle of Westray has become a ruin, the castle of Sorn has had a happier history, in that it has been carefully preserved, and century after century has been the home of noble and patriotic Scottish men and women.