There are Monaghan's in the British Telephone book for
The earliest census substitute is the Tithe Applotmentswww.genealogy.nationalarchives.ie
but there doesn't appear to have been a Tithe survey in Fermanagh as everything I look for comes up a big fat 0. (Do you know the answer Elwyn?)
Next census substitute is the Griffith Valuation but it didn't happen in Fermanagh until 1860-1862 and by that time there were 148 Monaghan's, none living in a townland called Ferndale.
Try looking for the people who used to own Ferndale when it was lived in www.landedestates.ie
The link to the restaurant wasn't working and they did speak of hundreds of years of history?