William Johnston

I don’t see a Johnston household in Gortnagullion in the 1901 census:

http://www.census.nationalarchives.ie/pages/1901/Fermanagh/Drumkeeran/Gurtnagullion/

Nor in 1911:

http://www.census.nationalarchives.ie/pages/1911/Fermanagh/Drumkeeran/Gortnagullion/

Nor is there a Johnston household listed there in the Valuation Revision records 1882 – 1898.

What evidence have you found linking the family to that townland?

ATM47,

The 1893 marriage certificate tells us that Patrick was a labourer (as was his father). He was evidently living in Gortnagullion then but it may not be where was born.  Labourers moved around a lot to follow the available work. They can be difficult to trace. Often their houses were of too low a value to appear in the land records, and often they didn’t stay in one place long enough to be recorded there.

https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_re…

I see Patrick was a widower. Have you found his first marriage? That might give a different townland.

Labourers generally weren’t landowners. The James Johnston you mention who was a landowner is likely to be a different family.