I think Armag is probably Armagh, the pronunciation is almost the same and most people couldn't write and so spelt things
phonetically. Its just that Antrim is another county. I thought perhaps there was an Antrim village or town in Armagh but I couldn't find anything to support that notion.
Even by the census in 1901 you would be surprised how many people couldn't write. Catholics for a long time under British Rule were not allowed to go to school and the Protestant church was dominant and RC relagated to chapels.