Hi,
Altnagarron is a small area just to the South-west of the townland of Ballymoney. It is to the south of the junction of Mullaghmeash Road and Altnagarron road. If your McCloskeys were of the Roman Catholic faith the nearest church would be St. Peter and St. Pauls in Ballymoney, nowadays called Foreglen, a hamlet off the main Londonderry/Dungiven road.
Regards