Dew developed in fog in part of America (7)
I believe the answer is:
midwest
'part of america' is the definition.
(I know that Midwest is part of United States of America)
'dew developed in fog' is the wordplay.
'developed' indicates an anagram.
'in' is an insertion indicator.
'fog' becomes 'mist' (mist is a kind of fog).
'dew' anagrammed gives 'dwe'.
'dwe' going inside 'mist' is 'MIDWEST'.
'in' acts as a link.
(Other definitions for midwest that I've seen before include "Mist dew (anag.)" , "North central region of the United States" , "Central part of US" , "US states including Illinois" , "American region" .)