Just received the marriage cert of William Alfred Thornhill m 1883 in Invercargill,New Zealand.

William was 28 and born Cork, Ireland. William was a laborer.
Father was John Thornhill Clerk(no place of birth given).

Mother was Margaret Moore(no place of birth given).

Where and how do i start researching in Ireland for Hubby's Family with so little information. Can someone point the Way

Regards Carol in New Zealand.