James Douglas born in Dundalk 1801

Hello, I am researching my husbands family and have hit a brick wall with James DOUGLAS who states on all census records he was born in Dundalk Ireland. He was by this stage living in Oxfordshire. 

Unfortunately he was not required to give fathers name when he married. 

I have searched every online website I could find trying to locate him. I am wondering if he was child of a british serviceman stationed there but no luck on finding a clue on Fold3.

Only other clue I have is that he lists a woman as his mother in law on one census who in fact isn't the mother of his wife and he is a batchelor when he married. I'm assuming she was his stepmother. She had remarried but her surname used at marriage was Douglas. She lists herself as being born in Norfolk. 

Any help in finding other records I can search would be gratefully accepted, even if they are records I've already searched. 

Thanking you

Diana