The Castle was built by the Lockharts.  The Lockharts was a family of ancient standing and the first record of the family is in the old ragman roll (1297) which tells us of Malcolm Lockhart del conte de air, possibly the progenitor (Ancestor) of the Lockharts of Barr.  The Lockharts had considerable ramifications (Having many branches) in Ayrshire during the 16th and 17th Centuries and they were amongst the leading Citizens, being merchants of no small enterprise in the Burgh of Ayr.

In 1390 Andrew Lockhart of Barr also had a charter of Lands.  GALLARTLANDS, MAKISWODEIS  AND NEWTOUN IN THE BARONY OF WATERS KYLL, granted by Robert the Third.  We learn in 1417 John Locarde-de-le-bar, was one of the jury in dispute between the burgh of Irvine and Francis of stane over a piece of moor ground, the paper containing the decision is kept in the archives of Irvine.

In 1561 James Lockhart is mentioned by John Knox, that the young laird of Barr was a traveller in the affair of a projected marriage between Queen Mary and the King of Sweden. James later married the daughter of Muir of Rowallan. In the year of 1636 George and John Lockhart signed the National covenant, a cause which many local people would die for; we also find at this time that John McCubbin and John Caldwell were servitors to the land of Barr.

Sadly in the year 1670 almost 400 years the Lockharts gave up its seat of Barr in Galston, The Barr Castle would play a poor part in the hearts in the people of Galston, soon it would be used as a Jail, a hospital, a wood store, wool store, a church, even the ancient barr tree (The Warrior Tree) would be taken away from her, what a way to treat that grand old lady