Polkelly Castle, later Pokelly, was an ancient castle located in the medieval free Barony of Polkelly. The castle is also recorded as Powkelly, Pockelly, Pow-Kaillie, Powkellie, Ponekell, Polnekel, Pollockelly, and Pokellie.

Prior to the 1390s the evidence suggests that the lands of Polkelly were in the hands of the Comyns family. The estate was important to the Lairds of Rowallan as it gave uninhibited access to the large and important grazing lands of Macharnock Moor, now Glenouther Moor. In 1512 the feudal Barony of Polkelly comprised Darclavoch, Clonherb, Clunch, with it's mill, Le Gre, Drumboy, the lands of Balgray, with its tower, fortalice, manor, and mill, and the common of Mauchirnoch (Glenouther). Records show that when the Mures held Poolkelly it extended to 2400 acres, two-thirds of which were arable. The origins of the lands of Polkelly and Rowallan as a unit may date back to the British period of the Kingdom of Strathclyde, as indicated by certain anomalies and coincidences in the boundaries of these lands.

Polkelly became the secondary power centre within the feudal Barony of Rowallan. It became of minor importance when Balgray became the principal home of the free barony of Polkelly in 1512. The castle lay close to the Balgray Mill Burn and its remains were finally removed in the 1850s, being used to create a road, only leaving behind the earth mound or motte, measuring 23m by 16m.

Sir Gilchrist Mure was one of the first to hold Pokelly, however he had to shelter there until the King was able to subdue Sir Walter Cuming and his followers who had seized Rowallan Castle. For the sake of peace and security Sir Gilchrist married his daughter Isabella to Sir Walter. In 1399 Sir Adam Mure held the castle and upon his death it passed to his second son, the eldest obtaining Rowallan. The lands of Limflare and Lowdoune Hill were included in the inheritance.

The castle and Barony of Polkelly was mainly held by the Mure family, however Robert Mure of Polkelly had died by 1511, leaving his daughter Margaret, Lady Polkelly, as the sole heir. Margaret married Robert Cunningham of Cunninghamhead in March 1512. The stars of the Mures were added to the armorial bearings of the Cunninghams. After 50 to 60 years the family sold Polkelly to Thomas Cochran of Kilmaronock and in 1699 it passed to his brother William. David, the first Earl of Glasgow then acquired the property and it was held by James, Earl of Glasgow in the 1870s. In the 1860s the ruins are described as being of ''the strong house of Polkelly''.

Tensions arose between the Cunninghames and Mures over their rights regarding grazing, etc on the very large and valuable area of common grazing to the north of Polkelly known as Machirnock or Maucharnock, now Glenouther. A royal letter of 1534 states that the Cunninghams had not been invested in the moor and it was decided that the grazing was split between Polkelly and Rowallan. In 1594 William Mure of Rowallan complained of the excess of Polkelly's grazing cattle and geese on the moor. Tensions had not arisen earlier as previously Polkelly was passed to younger sons of the Mures upon their marriage and this came with an allocation of rights on the moor.

A David Poe is recorded as being of "Polkelly, a farm bordering Fenwick and Stewarton, seven miles from Irvine". this David Poe, an outlaw and covanter of Ayrshire in 1666 who escaped to Ireland and had children there, is a likely ancestor of Edgar Allen Poe.