The town was once part of a district called Conmaicne, also known as Conmaicne Dúna Móir. It was also known as Conmaicne Cenél Dubáin, after its ruling kindred.
The area came under the rule of the Uí Conchobair in the 12th century, and was for a while the capital of the king of Connacht, Tairrdelbach Ua Conchobair, who died there in 1156.
Until the early 1980s, the N83 through Dunmore was on the main road from Sligo to Galway City. Improvements to the N17 route through Knock and Claremorris reduced the amount of traffic on the N83.
