First recorded in the Annals of the Four Masters as Daingean Bona Cuilinn, the site witnessed dramatic events in 1145 when the original fortification was burnt to the ground. The antiquarian John O'Donovan identified this location in the 1830s, connecting the modern townland name to its medieval predecessor. By the late 16th century, the rebuilt settlement, then known as Dangen I Beirne, had grown prosperous enough to host an annual fair each 25th May.

The O'Birne family controlled Dangan through the turbulent early 17th century, with Donogh O'Birne and later his son, also named Donogh, maintaining ownership of the lands. The younger Donogh held a quarter of the estate, comprising 160 acres, when the 1641 Rebellion swept across Ireland. Interestingly, despite its strategic location, Dangan doesn't appear in the chronicles of the powerful Mac Dermot clan who ruled much of Moylurg, suggesting it remained under the O'Birnes' independent control throughout this period.

Today, nothing remains visible above ground in the pasture where the castle once stood, though Ordnance Survey maps from 1837 and 1911 carefully marked its location for posterity. The site sits in low-lying countryside typical of this part of Roscommon, with only a gentle elevation hinting at its former importance. About 40 metres to the west, an ancient rath or ringfort provides a tangible link to the area's even deeper past, suggesting this spot held significance long before medieval lords built their towers here.