Simpleton I name in northern New York (5)
I believe the answer is:
ninny
'simpleton' is the definition.
(ninny is a kind of simpleton)
'i name in northern new york' is the wordplay.
'name' becomes 'n' (common abbreviation e.g. on forms).
'in' indicates putting letters inside.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'new york' becomes 'ny'.
'i'+'n'='in'
'n'+'ny'='nny'
'in' put into 'nny' is 'NINNY'.
(Other definitions for ninny that I've seen before include "Silly billy" , "dope" , "Stupid foolish person" , "Fool" , "gravely so miscalled by mechanicals" .)