The most likely source of any record on the Jackson family may be church baptism and marriage records. The records may not exist, or if they do exist, they may not be on-line.
You haven't said what denomination the family was. Clogher Church of Ireland has baptism and marriage records from 1804 onwards. Aughintain Presbyterian has baptism from 1836 onwards, marriages don't start till 1845. Carntall/Clogher Presbyterian has baptisms from 1819 and marriages from 1829. I am not aware that any of these records are on-line anywhere but there are copies on microfilm in PRONI (the public record office) in Belfast. Personal visit required to view them. If you can't get there yourself you might employ a researcher.
Bear in mind that marriages and baptisms may not be in the same church. Tradition was to marry in the bride's church after which she'd attend her husband's.
The name Sally is a diminutive of Sarah, so bear that in mind when searching.
I checked Griffiths Valuation for Aughintain c 1860. There were no Jackson or Mills households listed there then. None in the tithe applotment records c 1829 either, though the surnames were prevalent in the parish.
