This is an excellent example of a raised peat bog of the Irish Midlands. The Bord na Móna drains on the bog were blocked in the 1990s in an effort to rehabilitate the bog as peatland reserve; one of a network of such reserves in Ireland.
The bog is believed to be 9,000 years old and has formed in a basin between two east-west trending eskers. Mongan Bog has been taken into the care of An Taisce, and established as a reserve in 1987.
Typical Irish Midland raised bog vegetation exists. Sphagnum bog moss, the species that causes bog growth, is found in the wetter area to the centre of the bog. Mongan Bog has a notable lichen community due to the lack burning on the high bog in the recent past.
There are a good number of wintering Snipe to be found, however, Greenland Whitefronted geese no longer use this bog to the extent that the did in the past. Hen Harriers occasionally hunt over the site in wintertime.
The bog can best be reached from the Clonmacnoise to Ballinahown road, the R444, with parking at the Bord na Móna rail underpass. Panoramic views of the bog may be seen from the Pilgrim's Road to the north of the bog.