If Mary Polly Mason b abt 1775 was married to William Dungan b about 1777-1779, she would have been born in Delaware because her younger brother and second child of Isaac Mason and Parthenia Hall wrote a letter in 1860, and a transcription of that letter was later published by THE AMERICAN HISTORICAL MAGAZINE VOL. III JANUARY 1898 NO. 1 PG. 88.".....I was born in the State of Delaware, Revet Cy, in the year 1778..." (upper case K in old script was sometimes closed at the top)--Kent County Delaware. Mary Polly Mason is said to be the first child of Isaac Mason and Parthenia Hall, andParthenia seems to be unmarried at the time of her father's will in Kent County Delaware in 1772.
Could you give the Dungans who were born in GA?Some of Nathan Dungan's (of Wm & Mary Polly)children were sent to Alabama after Lilias Hamilton's death, but I don't show anyone from Georgia.
The Genealogy Bug's website that tracks Duncans has much Dungan information on it, especially for Madison County TN in 1850.