Thomas Walsh, who is from Dublin, wrote this tune which was poularised I think firstly by Buttons & Bows (Seamus & Manus Maguire on Fiddles, Jackie Daly on Accordeon and Gary O Briain on strings (Mandocello mostly)). If there are lyrics they are new and they are not widely known.
There is a song called Inisheer which is in Gaelic although I think there's an English translation as well - but this is a totally different tune - I think the tune of this one is scottish or it sounds like it to me. So this might be the cause of a bit of confusion. I don't have the lyrics but I think it contains the line - An tOilean aileann Orga Inis siar - the beautiful golden island of Inisheer.