What's coming up on the first of September in nouveau riche county? (8)
I believe the answer is:
cheshire
'county?' is the definition.
(I've seen this before)
'what's coming up on the first of september in nouveau riche' is the wordplay.
'what's coming up' becomes 'eh' (I am not sure about this - if you are sure you should believe this answer much more).
'on' is an insertion indicator (as in clothing 'on' a person).
'the first of september' becomes 's' (est letter of 'september').
'in' is an insertion indicator.
'nouveau' indicates anagramming the letters (a new order - 'nouveau' is 'new' in French).
'eh' enclosing 's' is 'esh'.
'riche' is an anagram of 'chire'.
'esh' inserted inside 'chire' is 'CHESHIRE'.
(Other definitions for cheshire that I've seen before include "Cat with broad smile, from English county" , "division in England" , "Type of English cheese" , "Crumbly type of cheese" , "Crumbly cheese from English county" .)