Findem, Boyd's Marriage Index has been online since about 2003/2004. Originally hosted on behalf othe Society of Genealogists (who own it) on Origins.net (which was taken over by FindMyPast last year), the SOG moved it to FindMyPast in about 2011. Its searchable here -
http://www.rootschat.com/links/01fhh/ - for anyone with a subscription or pay per view credits. It is also viewable on the SOG website's Members Area.
That said, it isn't particularly good post 1700 for any county, and coverage for Essex is patchy from my experience anyway. Coverage is best for Cambridgeshire, Suffolk and Norfolk, but not complete even up to 1700 for these counties. The reason the SOG own the Index is because it was created by one of their founding members, Percival Boyd. It is, though, a useful resource.
There is no marriage for a Matthew and Elizabeth Cooper at around the correct time on Boyd's, I've had a look.
Nannyj, your profile doesn't say where you live, but if you are in the UK, you might want to consider paying for a search on Jack Baxter's Essex Marriage Index which I believe is pretty much complete from 1754 to 1837, excluding entries that are on Boyd's for that time period. Mr Baxter is no longer running the service, but details of the search service are here -
http://www.sturnidae.com/Essex/MarBur.htm. It used to cost a £1 per marriage, but there are no details on the webpage now, you have to contact the new hoster for details. According to the Dec 2014 edition of the Essex Family Historian (ESFH journal) the cost at the point was the same. Hopefully, its not gone up since then.
Even if you aren't in the UK, its worth an email to ask as they may now have different payment arrangements, it used to be a sterling cheque or similar.
