Innishannon derives it's name from" Inis Owenane" - Little Owen's Inch - the Inis or Inch being the flat strip of land along the River Bandon, now partly occupied by the village of Innishannon.
The town of Innishannon grew around the Ford (a shallow place in the river where people and their goods could cross) known locally as "Bóthairín an Átha". At one time Innishannon was considered "a place of importance" - being the gateway between Cork Harbour and West Cork. The earliest mention of Innishannon is in the Book of Leinster, which states "The Danes plundered Dun Dearmaighe (Dunderrow) and InisEoghanain (Innishannon) in the year 837. An entry in the annals of the Four Masters refers to the arrival of the Normans in 1202 and that Donal Mór MacCarraig defeated the Gall at Innishannon and many other battles.
In 1240 Henry III granted the town and ferry of Innshannon to Philip DeBarry and also the right to hold fairs there. In 1262 Finian McCarthy of Ringrone burned the DeBarry property at Innishannon.
In 1412 Henry VI granted a charter to the De Barrys. In the grant, Innishannon is described as a place of considerable importance, being a large walled town and a warf and many castles. In 1476 De Barry build Dundanier Castle .
The annale entries for the years 1489 and 1493 show that Raymond DeBarry Abbot of Traction Abbey and Parish Priest of Tracton, bound himself for the rectories of the Parish Churches in Innishannon and Dunderrow.The local landlords (Feudal Lords) of the time nominated candidates to be in charge of eccleiastical affairs of his manor. Barry Oge was the Feudal Lord of Innishannon. The Barrys have association with Wales were instrumental in founding the Cistercian Abbey at Tracton in 1224. The Monks came from Alba Tractu in Wales. The Cistercians seemed to have control of religious affairs of the Parishes in the De Barry manor. The churches at Innishannon (Old Tower) and Dunderrow were regarded as Churches of ease of the Abbey.