Ireland/Northern Ireland Gibsons

I found ancestor Rev. Alexander Gibson of Mullingar, Westmeath, Ireland. He was the first minister sent to the local Presbyterian church in Mullingar from 1823-1858. He was licensed in Letterkenny, Northern Ireland. I have only found him mentioned in 2 daughter's marriage records, some church notes, Griffith's Valuations, local directories & interesting detail in the Irish Encumbered Estate Rentals in 1858. I am descended from his daughter, Elizabeth Gibson, who married Austin Cooper, a widower with a baby son. Austin & Elizabeth had 12 more children. Does anyone have info on this Rev. Gibson or recommendations as to where I can find more info on his family? thanks