The ruins of the castle lie a short distance from Howwood in Renfrewshire in a private garden on a minor road between the A737 and the B776.

The new barony was held by William, Lord Sempill and the principal dwelling or messuage was Castle Semple.

[5] In 1505 James IV of Scotland visited John Sempill's at Elliston his collegiate church at Castle Semple to which he gave an offering of 14 shillings.

[9] An interesting story is told of how the Sempill's came to hold the 'Lands of Sempill' that circa 1316 involves Marjory Bruce, daughter of Robert the Bruce and her son, Robert II : - "In this shire, at a part called the Knok, on Greiff near Ranfrow, was King Robert, called Blear-eye, cutted out of his mother's womb by Sir John Forrester of Elliestoun (who being hazarded on extremity to use that remedy to preserve the child's life, the Queen having there taken her child ill, being on the fields and dying, the child being quick in her belly) who before that was reputed a simple man – from whence the House of Sempill and Lords thereof have their name, and a part of their estate.

A memorial cairn now stands on the spot where the heavily pregnant Princess Marjory, wife of Walter Stewart, 6th High Steward of Scotland, is said in some accounts to have fallen from her horse and broken her neck.

[14] The tower of Elliston guarded the important land route to the south at a time when no road existed closer to Lochwinnoch.

The old road continued up the valley side to run past the castle, then across the neighbouring fields before entering via Low Howwood along the remaining section of the road that then runs passed Glenfall House (Aitkins whinstone Quarry site), originally continuing on to George Street across land now built on; George Street has therefore become a cul-de-sac.

The house is on the grounds of Principia College and named after "'Elliestoun Tower' on Castle Semple Loch".