Loudoun Kirk is a disused church located about one mile west of Loudoun Castle.  Since 1994 the kirk and grounds have been preserved by a local charity, ''Friends of Loudoun Kirk''. The Friends of Loudoun Kirk completed a survey of the headstones and plaques found within the graveyard. Loudoun Kirk is the earliest known site of Christian worship in the area, having been founded in either 1198 or 1451. At or soon after its foundation, the revenues of Loudoun Kirk, were allocated to support the monks of the newly founded Kilwinning Abbey, they were however required to provide a priest to attend to the spiritual needs of the parishioners.

During the Campbell verus Kennedy feuds of 1527/8, Loudoun Kirk was badly damaged, but rebuilt. In 1530, because of the shift in population, a chapel was built at Newmilns. Loudoun Kirk remained the parish church until at least the 17th century, at which time the chapel in Newmilns was upgraded to parochial status. Loudoun Kirk and its kirkyard continued in use for occasional church services, but more particularly as the last resting-place of generations of the parishioners of Loudoun. A carved panel on the building records that it was repaired in 1898 by the Third Marquis of Bute.

During the Covenanting times (1638-88), the Rev. John Nevoy of Loudoun Kirk was the chaplain to the Covenanter army led by General Leslie who were fighting the Irish MacDonnels who had invaded the west of Scotland. In 1647 the fortress of Dunaverty was taken and at Nevoy's urging the entire Irish garrison were driven over a cliff to their deaths. Loudoun Kirk's vault and surrounding graveyard served as a burial site for both Loudoun's nobility & locals. Amongst those interred are John Campbell, 1st Earl of Loudoun, John Campbell, 4th Earl of Loudoun, the tragic Lady Flora Hastings, the poet Janet Little, known as ''The Scottish Milkmaid'' and Thomas Fleming, a Covenanter, killed at the Battle of Drumclog.

Francis Rawdon-Hastings, 2nd Earl of Moira and Marquess of Hastings, died in 1826 aboard H.M.S. Revenge off Naples and following his directions his right hand was cut off and buried with his wife, Flora Mure-Campbell, Marchioness of Hastings and 6th Countess of Loudoun, the second daughter of James Mure-Campbell, 5th Earl of Loudoun and Lady Flora Macleod. This wish was complied with, and his hand now rest clasped with hers in the family vault.

The Loudoun Kirk dead bell still survived in 1894, having originally been sent to the parishioners from Holland by the 2nd Earl of Loudoun. It had ''Loudoun Kirk'' cast in raised lettering and was used at funeral processions; it was held by Mrs Semple at Loudoun Village in 1875. The old kirk is situated next to the site of the villlage of Loudoun. The village was last occupied by local miners, but after the Second World War the houses fell into disrepair. With no mains gas or electricity supply, the residents were moved into the new houses in Galston and the village was abandoned. Foundations of the cottages can be seen in local fields close to the lane. A plan to build a new village in the 1990s came to nothing.