Kilmanaghan, 'the church of Monaghan' or 'the wood of monks' is bounded on the north by Kilcrumreragh and Horseleap and on the south by Rahan and Lemanaghan. St Manchan founded Lemanaghan around 645AD. The larger monasteries were independent and they had control over a number of smaller ones which were founded from it. These federations of monasteries were referred to as "paruchiae". Kilmonaghan would have been one of the smaller ones affiliated to Lemanaghan which s only about 6 miles away.
Little is known of the origins of Kilmonaghan Church at the present time. A carved fragment, which indicates late Celtic influence, lay inside the ruin for many years, while the early Celtic stone found in a cleanup in the sixties poses the possibility of an earlier structure. These disappeared in the early eighties. The design of what remains today suggests late seventeenth century or early eighteenth century.
The existing church ruin is a plain quadrilateral approx 60ft x 30 ft. At some stage it may have had a cut stone ogce cornice supporting the wall plate and a matching door case. However over time many of the stones were removed and used as grave markers
When the church was being repaired ca 1690 it is speculated that the established church took over the site and carried out major remodelling and repairs at that time.
The Parish (Kilmonaghan) and the old cemetery and church in Kilmonaghan all get their names from St Manchan. The saint originally hailed from Mohill, where he founded his first monastery.
During a visit to that great centre of learning, Clonmacnoise, Manchan was granted lands at Leamonaghan in order to establish a monastery there. He did this, and died there of the 'Buidhe Chonailp' - the great plague, in 664. After his death the place was called Liath Manchain - Manchan's Grey Land. Some of his bones are preserved in a Shrine in Boher Church.
Tradition has it that St. Manchan was a tall man who walked with a limp and this was verified some years ago when the Shrine, with its contents, was sent to the British Museum for refurbishing. The bones were examined by experts, who pronounced them as belonging to a tall male, who suffered from arthritis. Many stories and legends exist about the saint's life, whose feastday is on 24th Jan.
The Graveyard contains 112 memorials that have visible inscriptions. There are also some 28 un-carved rough stone pieces, acting as Markers. Local knowledge indicates that there are numerous other burials here that have no Memorials or Markers. The majority of the memorials are headstones made of limestone with Roman incised inscriptions. The remainder are made up of Table-Tombs and Ledger Slabs. There are two Celtic Crosses and one Obelisk. The symbol I.H.S. with cross appears on the majority of the memorials. All Memorials face east. With the exception of no 122, which faces west.