Found the birth of William John McCallion to above parents in 1866 in Ballyloughan, near Moneymore. Father’s occupation farmer.
https://www.irishgenealogy.ie/files/civil/birth_returns/births_1866/03512/2291777.pdf
Griffiths Valuation for 1859 lists Edward McCallion on plot 2 in Ballyloughan. Just under 18 acres. Today that farm is on the Drumrot Rd. Looking at it on a satellite image, I’d say it is still a farm but has been combined with plot 1.
Probate abstract:
Letters of Administration of the personal estate of Isabella M'Callin otherwise M'Callion late of Ballyloughan County Londonderry Widow who died 13 January 1892 at same place were granted at Londonderry to William John M'Callin otherwise M'Callion of Coagh County Tyrone Merchant the Son.
This looks to be the same family:
Letters of Administration of the personal estate of Edward Joseph M'Callion late of Cough County Tyrone Merchant who died 26 April 1889 at same place were granted at Armagh to Edward M'Callion of Ballyloughan County Londonderry Farmer the Father.
Edward junior was a Merchant. He was a bachelor.
https://www.irishgenealogy.ie/files/civil/deaths_returns/deaths_1889/06144/4755420.pdf
The Valuation revision records show that after Isabella’s death in 1892 the farm transferred to a Mrs William Millar.
Marriage for an Isabella McCallin in 1884 whose father was Edward, a farmer. She lived in Coagh, so possibly she’s a member of this family:
https://www.irishgenealogy.ie/files/civil/marriage_returns/marriages_1884/10908/5984646.pdf