It does look like this could be a medal of (or around) 1821. It's issue coincides with the beginning of reign? - Very likely! For coronation? - I doubt it! They do a number of special coronation medals (much more attractive!).
I'm not sure what the (contemporary) demographic for this type of artifact would be; it's a very curious one, though!
There's a couple of things I find interesting:
1) While the title is "Population of the British Empire" they itemize the British Isles only and lump "India and other foreign possessions" together.
2) Look at the precision of the census, down to the singles, except Ireland - 5,500,000, and Dublin - "no estimate". It's as if they didn't dare to venture into Ireland and took a pretty general "guesstimate" on it.