Hessilhead is in Beith, North Ayrshire, Scotland. Hessilhead used to be called Hazlehead or Hasslehead. The lands were part of the Lordship of Giffen, and the Barony of Hessilhead, within the Baillerie of Cunninghame and the Parish of Beith. The castle was situated at grid reference NS380532.

In the late 19th century, the castle was described as "now roofless and ruinous, is an oblong structure, built at two periods, measuring some 74 feet (23 m) by 38½ feet. The old west part was apparently a 15th-17th century keep; the east addition was built by Francis Montgomerie, who bought the estate in 1680. Both old and new parts are vaulted on the ground floor; the upper parts are too ruinous to describe. The mansion was allowed to become ruinous about 1776." It was noted by Pont as a strong old building, surrounded with large ditches and situated on a loch.

An article in the Kilmarnock Standard of August 1949 titled Ancient Ayrshire Castles is accompanied by a photograph that shows substantial ivy-clad ruins set in a garden landscape with lawns, shrubs, trees and a well maintained paths. In 1956 the Royal Commission recorded that Hessilhead Castle has been demolished. Extensive quarrying around the site has removed any possible traces of a moat. No building vestiges remain.; this is however inaccurate as traces of rubble and foundations are still visible on the site, and the drainage from the quarry does use what was once a moat. Timothy Pont in around 1604 records that the castle was protected by substantial ditches and stood on a loch. This loch has long since been drained and the ditches filled in.

William Roy's map of 1747 - 55 shows a farm town of Hazlehead and nearby, set amongst fairly extensive ornamental rides and plantations, the castle of Heeselhead (sic). Armstrong's map of 1775 marks Hazlehead and finally John Thomson's map of 1832 gives the farm town of Hazelhead and the ruins of Hazlehead.

Hessilhead in its later days was occupied by the family of Lord Glasgow, and after they left, the proprietor, a Mr. Macmichael, about the year 1776, took off the roof and allowed the place to go to ruin. Circa 1887 - 92 it is described as being enclosed as a garden. Dobie records the despoiler of Hessilhead as a Mr. Carmichael, who sold the materials from the castle and also removed parts of the walls, as well as cutting down and selling an impressive old Yew tree. In the 1960s the remains of the castle were blown up on the instructions of Howie of Dunlop.

Robertson records that Francis Montgomery of Giffin had added to the old square castle ..a great addition in a more modern stile. He also comments on the extensive tree planting that was in the shape of a cross, according to the taste of the times. It has been suggested that Coldstream Mill was built at this time and Robertson comments on the excellent lands of Cauldstream. Dr. Robert Patrick had planned to build a new mansion in the vicinity of the ruins of the castle and had already laid down the gardens.

Dobie also records that a little to the south of the ruined castle there was a singular echo, which slowly and plaintively repeated the voice once, throwing a melancholy charm over this scene of departed grandeur.

The first recorded holder of the lands of Hessilhead was Hugh de Eglintoun, who obtained the lands following forfeiture. Eglin, Lord of Eglintoun is the first of the family recorded, living during the reign of King Malcolm Canmore; he may have been one of the Saxon barons who accompanied King Malcolm (who died in 1093) on his successful return to Scotland. The family continued until Elizabeth de Eglintoun, the sole heir, married Sir John de Montgomerie of Eaglesham. Elizabeth's mother was Giles, daughter of Walter, lord high steward of Scotland, and sister of King Robert II.