Hello Michael,

My grandfather was Sylvester Cotter (born & died in Australia), and he was the grandson of a Michael Cotter who was born (to the best of my knowledge) in the Rathcormac - Fermoy area of Co. Cork in 1809. There is a Cotter Family DNA Project at Family Tree DNA - http://www.familytreedna.com/public/sonsofottar - where you might pick up some cousins.

Best wishes for your search
Dafydd