Carol, the principle Rea settlement in Down was in and around Drumskee and Edentroory, where my family lived during the 17th and 18th centuries. Later in the 18th century, some of my line went to Newry.
I'm a direct descendant of William Rea of Drumskee (1680-1785) and I believe his father and probably his grandfather also lived in County Down. There were Reas on the 1631 Muster Roll of County Down, taken at Bangor.
I have several Robert Reas in my database, a few born in County Down, but none born around 1805, that I know of.
My line moved to Newry from Drumskee sometime in the 1700s and they emmigrated from Newry to Pennsylvania in 1774, settling in Mifflin County, then Franklin County. They had cousins living in Cumberland and Bedford Counties, also.
My emmigrant ancestor's brother Samuel emmigrated earlier, perhaps before 1750. He had a brother named Robert, born in Drumskee between 1735 and 1740 and I don't know anything about his descendants, but he could have emmigrated, as well and might have had a son or a grandson named Robert. His brother Matthew (my g-g-g-g-grandfather) also had a son named Robert, who, in turn, named a son Robert, so it's a fairly common name in my family during that period. I mention Samuel's line as one of his descendants (maybe several) wound up in Pittsburgh, including Samuel Rea, the President of the Pennsylvania Railroad.
Anyway, if you're searching Dromore, Drumskee and Edentroory are the most likely places.
Gary Rea