Trying to see where my ancestors came from in Ireland

I have been able to trace my family line to a Charles Cavanugh born in 1806 in Christian, Kentucky.  I have been able to find out that his parents were Charles Cavanaugh and Elizabeth.   I have not been able to see if Charles and Elizabeth were born in Ireland, and immigrated to Kentucky before Charles was born in 1806, or if another ancestor before Charles the first was the one who came from Ireland.   I know from DNA results that my Mother is 23% Irish so we know our ancestors came from Ireland at some point.  Does anyone know how I can trace someone in Ireland before 1800?