In any research I have done in the past for folk from Ireland who ended up in Campbeltown, they often came from places along the Antrim coast, directly opposite the Kintyre peninsula. So Ballycastle, Ballintoy, Cushendun, Cushendall & Glenarm. As Skoosh has said folk there were back and forth to Scotland all the time. It’s only about 12 miles across at the closest point and folk from north east Antrim used to attend fairs in Campbeltown and Inverary etc, sometimes later featuring in the Sheriff court as a result of misbehaviour involving drink. Until the Antrim coast road was built in Victorian times, those coastal communities were very isolated and it was easier to do business in Scotland than it was to get to Belfast or Dublin. So there was a lot of contact with Kintyre. And of course a lot of the inhabitants of the Glens came from Scotland originally anyway. There was a huge influx in the late 1500s and early 1600s when the MacDonalds of Islay were granted a quarter of county Antrim and settled the north east corner. The McDonnell (as it is spelled in Ireland) family seat today is Glenarm Castle, where the Earl of Antrim resides. The MacDonalds took thousands of tenants from their Scottish estates in Islay, Jura, Kintyre and elsewhere with them. Which is why the Gaelic spoken in the Glens of Antrim is/was noted to be identical to Scottish Gaelic, and not the same as that spoken in say Donegal, which is a different dialect.
But getting back to Duncan born c 1785, the problem you face is that none of the parishes for the places I have mentioned have any baptism records for the late 1700s, so even if you identify where he came from, and you know his denomination, you may struggle to find any record of him.
I agree that the name Duncan sounds more Scottish than Irish but it is found in Ireland, especially along the north coast (for the reasons I have explained). If you search the 1901 Irish census, there were 246 people with the forename Duncan. 76 lived in Co Antrim. Some of those were born in Scotland but excluding them there’s plenty more, many of whom lived in places like Ballintoy, Dunseverick, Cushendall etc, along the north east coast. So your Duncan could well have been born in that area. But I’d say his forebears came from Scotland originally.
