Several buildings occupied this site and it is not known when the present church was built. The site of the parish church was the same when the Down Survey was made in the 17th century. It was the church of the Edgeworth family. The spire was built on the ground on an iron frame and covered with slates by Richard Lovell Edgeworth in 1811 and then brought to the top of the tower by a system of balancing pulleys. It lasted until 1935. A wooden gallery was erected about 1784 for the benefit of poor parishioners. This was removed in 1888 when further reconstruction was carried out at a cost of £450. Final repairs were made in 1957 after storm damage and dry rot in the timber. Inside are memorial tablets in memory of many of the Edgeworths – one mentions Admiral Beaufort who devised the scale to measure wind force which is used in weather forecasts to the present day. The adjoining cemetery contains some interesting graves apart from the Edgeworth vault. These include Dr. Thomas O’Beirne (1739- 1747), Catholic Bishop of Ardagh, who may have been from Mullagh or Mostrim, and nearby are those of two Vicars General. One was Rev. Francis Ferrall, Pastor of Ardagh and Mostrim, the other being Rev. F. John O’Rorke, parish priest of Mostrim, a Franciscan of the old Friary of St. John Baptist. He died in 1793. Oscar Wilde's sister Isola is also buried here and though the old headstone has disappeared a new one was erected in 2013. The last person to be buried there was Conal O’Ferrall of Camlisk who died in January 1933. The cemetery was officially closed about 1896 when the present one was opened at Aughafin.