Hello Duane:
I could not find any references regarding a place known as Southwell. The Mormon Church archives list John's place of birth as Derbyshire, Sutton on the hill is located in Derbyshire so you are probably correct but I can not find anything to prove that. I believe his place of birth in his profile should be listed as Derbyshire but I'm not the curator of his profile and can not update his profile..
Greg