In 2003 COC had 27 local departments and 24 associations. (For example: Purmerend was part of COC Amsterdam.) Before, the older list online, they had two association (or locations) more: COC Noord en Midden Limburg and COC Zeeuws-Vlaanderen.
This was the (already declined) list in COC Update from June 2003:
Arnhem (COC Midden-Gelderland)
Bergen op Zoom
Den Bosch (COC 's-Hertogenbosch)
Den Haag (COC Haaglanden)
Den Helder (COC Kop van Noord-Holland)
Deventer (COC IJsselstreek)
Enschede (COC Twente/Achterhoek)
Groningen (COC Groningen & Drenthe)
Haarlem (COC Kennermerland)
Hilversum (COC Midden-Nederland)
Leeuwarden (COC Friesland)
Maastricht (COC Zuid-Limburg)
Middelburg (COC Midden-Zeeland)
Oss (COC Brabant Noord-Oost)
Purmerend (COC Amsterdam)
Utrecht (COC Midden-Nederland)
Zoetermeer (COC Haaglanden)
Today, COC has 20 associations and 21 locations. Breda and Tilburg are one, but on their website I still see a location in both cities.
Today's list (as on their website coc.nl):
Eindhoven en regio
Groningen & Drenthe
Haaglanden (Den Haag)
Noord-Holland Noord (Alkmaar)
Noordoost Brabant (Oss)
Tilburg Breda e.o. (Tilburg & Breda)
West-Brabant-West & Tholen (Bergen op Zoom)
I'm not sure if COC has a decline in membership but I know the local organizations are having a hard time and one after another can't afford to bring up the money to rent an apartment. In that case they officially merge two organizations (and locations) into one. The smaller one just disappears.
The Dutch organization for sexual reform, NVSH, saw almost all their local organizations disappear and also almost all of their members. COC used to be open about how many members it had. The last ten years it's hard to find a number anywhere on the internet. In an article from 2004  it reads that in 2001 COC had 24 local organizations. All these organizations together had 8.000 members at that time. On the Dutch Wikipedia it says that COC still had approximately 8.000 members in 2012. But the Dutch Wikipedia always lacks references. In the 1990's COC had a record of 10.000 members . I can mail COC and ask how many members they have right now, but I dislike the organization. COC has become a hetero-normative organization. In my view they are not gay anymore. I wonder what will happen to the COC in the near future.
 'COC staat nu voor Crisis Op Crisis', www.volkskrant.nl/binnenland/-coc-staat-nu-voor-crisis-op-crisis~a723199/, Volkskrant, 17 June 2004
 Oud-COC-voorzitter Cees van Wijk overleden, www.coc.nl/algemeen/oud-coc-voorzitter-cees-van-wijk-overleden, coc.nl, 2012
3 August 2017