Bill,
I had a quick look at the Scottish censuses. I see from the 1861 census that though daughter Jane was born in Durisdeer, Dumfries in 1851, son James was born in Ireland c 1853. So it looks as though the family went back to Ireland around 1852 for a year at least.
I have searched the Irish RC church records on Ancestry but can’t find a marriage for Dennis & Jane, nor baptisms for Mary & James. That could be because they married and had their children baptised in a parish which doesn’t have any records for the 1830s. (Not uncommon). Most did have records by the 1850s but not all do.
I did find what looked like a possible baptism for Mary at St Macnissi’s in Larne on 26.3.1838. Parents were Denis McCormick and Jane (no maiden name). Sponsors were Patrick McLaverty and Catherine McFall. However that couple had 3 other children there in the 1840s ie Charles, Patrick (both in 1845) and Helen in 1842. And there’s no sign of a James c 1853. So it doesn’t appear to be the right family.
There’s a clue from Dennis’s death certificate, namely that his father Charles was a harbour master (and dead by 1871). Have you looked for him? To be a harbour master you normally had to have a Master’s Ticket (you certainly do these days). Might be worth checking maritime records for him. So a seafaring man who retired to run a harbour somewhere. So at a guess, the McCormicks lived near the coast! If there are websites that specialize in shipping and maritime records, they might be able to suggest where to search further. There’s a tree on Ancestry (All New Smyth tree) which has Charles McCormick’s wife Mary McDonald born in Cork in 1794. I’ll guess that’s your own tree but if it’s not you might want to check with the tree owner to see where that information comes from. No specific place of birth for Charles or Dennis – just Ireland.
I searched an on-line newspaper site for "Charles McCormick + harbour master” but without success.
Another approach might be to check Scottish Poor Law records. If your ancestors claimed under the Poor Law in Scotland (as many many Irish did), then the Poor Law file usually records their parish of origin in Ireland as well as details of next of kin there. My recollection is that Poor Law records for Ayrshire are held in the county archives office. Not sure about Dumfries but this site seems to have some:
https://www.oldscottish.com/durrisdeer.html
