The foundations of the ruined Ardrossan Old Parish Church lie on Castle Hill, to the north northeast of Ardrossan Castle. There was probably a church on this site before 1226. The church was destroyed by a storm in 1691, but was excavated in 1912 when it was shown to comprise a long, oblong building, with only 20cm (8 inches) of wall now visible. The chancel and nave were the same width, with the former raised above the latter by three low steps. Areas of stone flooring remain. The ruins are B-listed owing to their historical significance. A stone coffin, with a finely decorated lid, was found within the walls of the church. Thought to have belonged to a local baron who was a Knight Templar, it was taken to Ardrossan Town Hall and is now in the property of North Ayrshire Council Museums Service.
Groome (1885) suggests that a tombstone in its kirkyard is linked with a warlock baron, known as the Deil o' Ardrossan. It was said that if anything beneath stone was thrown into the sea a dreadful tempest to devastate that area, perhaps a clue as to the fate of the church. A few gravestones remain, one dated 1662 and some dating from the 18th C.
