The north transept was built about the 13th century. The piers of the aisle are also of Cataclewse stone. St Merryn Church has a 'wagon roof' built in 1422 and a tower with six bells. The 15th century church expansion included the addition of a south aisle of seven bays. The plaster coat of arms of Charles II, commissioned in 1662 by Harlyn House's Thomas Peter, is located near the tower. The church renovations occurred over two periods: once between 1887 and 1907 and again in 1962, when the west tower was rebuilt. The church became a Grade II building on 6 June 1969 and a Grade II* building on 20 May 1988.