Ballymahon

Ballymahon on the River Inny is a town in the southern part of County Longford, Ireland. It is located at the junction of the N55 National secondary road and the R392 regional road.
Ballymahon derives its name from the Irish language term Baile Uí Mhatháin or Baile Mathuna, meaning "Town of Mahon". This may refer to Mahon , a southern chieftain and the elder brother of Brian Boru, who is believed by some to have fought a battle in 960 in the vicinity of Ballymahon at Shrule where he defeated O'Rourke of Cavan and laid claim to lands in the area. This is disputed by others who claim Mahon may relate to a sub chieftain of the O'Farrells who ruled over this part of County Longford in the 14th century.

Wikipedia