I don't know much about Neo-Druidry, but I have found it interesting to look at the activity of groups throughout the world. Much of it seems rather informal, at least in the past. In some places in the South, which was settled largely by Scots and Scotch-Irish long ago, I have at least heard that there has been Neo-Druidic gatherings going back to at least the 70s. It was interesting to listen to some old accounts of this from a couple of YouTubers, especially since this was nothing that one would see on Wikipedia. Maybe it's just me, but the image of loosely associated Neo-Druids gathering in a heavy wood and brush area during the Summers in the 70s is an interesting visual. Perhaps something from genetic memory comes alive in people.
Not a lot is actually known about the actual practices of the pre-Roman Druids, so there is more of a need to distinguish between Druidry and Neo-Druidry. I have gotten the impression that it may have began thousands of years ago, and was something of a fusion of early native magical traditions mixing with Odinic traditions from early incoming Teutonic tribal groups in Western Europe. Druids were mainly in what is today the British Isles, France, and Germany. I don't know if the German Druids were from the ancient Celtic south, or perhaps from an eastward spiritual migration. It's possible that there may have been some elements of Druidism in what is today the Netherlands, Belgium, Northern Spain, and Northern Italy, but there doesn't seem to be much proof of that.
The first attempts at reconstructionism were in Britain during the seventeenth and eighteenth centuries. Some Freemason Lodges there developed a Druidic style to them apparently. Winston Churchill was a Neo-Druid, which perhaps came via this type of "Druidic-Freemasonry." At one point all of the British Isles were more culturally if not ethnically unified, and heavily Druidic. One of the greatest women in history, Boudicca, must have been a Druid. I found one very interesting website from the UK called The Order of Bards, Ovates and Druids. I love podcasts, and they have a lot of them, which you can see the link at the bottom of the page. I've only listened to the first three. There are interviews, music, story-telling, and more. It's been awhile since I listened. There are also links to apparently connected Neo-Druid groups in France, Germany, the Netherlands, the Czech Republic, Portugal, and Italy; and it appears that there will be ones in Spain and Russia. There could have been some Druidic elements in all of those places, except Russia I think. But, there were Celts in Poland, so who knows. The Italian group is called L'Ordine dei Bardi, Ovati e Druidi. YouTube is a great place to get a perspective of both Druidry and Neo-Druidry.
4-15-13 NOTE: Upon further study, Druidism was apparently also present in a few places in Scandinavia; although the center seems to have been the British Isles and northern Gaul.