Hello Tony, Your great-grandfather Rev. Wm. Thos. Dunn was a prominent Presbyterian minister in Sydney, Australia (St. Enoch's Church in suburban Newtown). His New South Wales death certificate should contain essential information; place of birth, parents' names and occupations and where married and to whom. Do you have this certificate? Australian researchers find that there is a great deal more relevant information to be found here than has survived in Ireland. To be successful in your search and receive assistance on this list it will be necessary to quote parents' names. Dunn is a rather common in Co. Tyrone. As Protestants, it may be possible to locate a record of William's parents' marriage - the registration of Protestant marriages in Ireland commenced in 1845. Looking at the online indexes to New South Wales deaths it looks as if his parents were named John and Margaret. Would this be correct? Trust this helps your search, Len Swindley, Melbourne, Australia