Outstanding independent region houses 2,000 people altogether (9)
I believe the answer is:
community
'people altogether' is the definition.
(a community of people)
'outstanding independent region houses 2000' is the wordplay.
'outstanding' is an insertion indicator (some letters standing outside or around others).
'independent' becomes 'i'.
'region' becomes 'county' (county is a kind of region).
'houses' means one lot of letters goes inside another.
'o000' becomes 'mm' (o000 in Roman numerals).
'i' put within 'county' is 'counity'.
'counity' placed around 'mm' is 'COMMUNITY'.
(Other definitions for community that I've seen before include "Fellowship" , "Association" , "Group of people living in a particular local area" .)