My guess is we should be looking in Dorchester Co., MD.There is a Zadock Jones there on the 1783 tax list (you can access an index to this list online at the Maryland Archives site).I have an old newspaper clipping which was recently sent to me (apparently published shortly after his 100th birthday in 1856), that states that Zadock Jones did indeed marry Elizabeth Flowers and that he was born in Maryland.
As you may know, Dorchester Co., MD borders Sussex Co. DE and parts of Sussex Co. were at one time considered to be in Maryland, so I don't know at this point whether Zadock moved from MD to DE, or the state line moved.(Of course, it could also be another Zadock in 1783 Dorchester Co....)
Zadock's son, Newton C. Jones, was my 2nd great-grandfather.I am currently compiling as much info as possible about Zadock's descendants and would love to include your line.Please e-mail me so we can compare notes.Thanks!!!