The ruined St Lonan's parish church is thought to be on the site of an early medieval keeill or chapel, which would have been in use between circa AD500 and AD1000.   Lonan Old Church is dedicated to the Irish saint, Adamnan of Iona, or the shortened version, 'Onan'.


The church fell into a ruined condition, but the eastern end has been restored for use as a place of worship.  The building is orientated east-northeast to west-northwest and measures 17.3 metres by 6.7 metres. The western 10.0 metres is now roofless with walls averaging 0.9 metres thick and generally to their original height with a doorway in the south and window in the west. 


The remainder has been restored and is walled off from the ruin and is used for divine service while burials have taken place quite recently in the surrounding grave yard. In the interior of the ruined portion of the church and affixed to the north wall are 6 crosses or portions of crosses from the surrounding area. They bear inset bronze plaques with their cross number and a notice dates them collectively from the 7th to the 9th century.