I am a direct descendant of the Penney's who lived in south Co. Cork (mostly around Kinsale) from at least the mid-eighteenth century to the early twentieth century. I have compiled a fair amount of data on them. The names Thomas, John and James have appeared in every generation. Given some more information I may be able to trace your ancestor Thomas Penney who was naturalised a U.S. citizen in 1861. I believe that the Penney's came to Ireland from England in the seventeenth century, but unfortunately the surviving Irish records are too fragmented to trace the family line back beyond the late eighteenth century.