The surname was actually Henigan in Ireland. John was born December 2 1870. His mother was Attracta Johnston.
He had a sister Mary born in 1872 see ninth record
Another sister Attracta and a twin brother Michael baptized September 30 1876 ( I did not locate the civil record).
I did not find the marriage record.
The 1855 Griffiths Valuation head of household listing for Killasser civil parish shows a Patrick Henigan in Tumgesh. Possibly this record is for the father of John Henigan or more likely maybe the grandfather of John Henigan.
Did the entire family emigrate?
Let me know if you have questions.