Ancient Celtic societies in northwestern Europe were organized by caste, much as Indian society is. Among the castes of the Celts was that of the Druids, the learned men and women of their time and place, called by the Greeks "natural philosophers." After the Roman conquest of Gaul under Julius Caesar, circa 60 B.C., Druidry was suppressed on the Continent and in Roman Britain, though it survived in a debased form in Ireland, Wales, Scotland, the Isle of Man, and in a few mainland pockets.
Druidry, with its twin emphases on ritual magic and adoration of nature, was never completely rendered extinct, though no one has yet demonstrated an unbroken Druid lineage in Europe. As the Enlightenment spread across Europe in the mid-1700s, Druidism underwent a small revival as a humanistic-ecological spiritual practice, a revival which continues today.
The first Druid group ("Grove") in the United States was The United Ancient Order of Druids, organized in New York City in 1830.
By 1930, this group had 35,000 members across the United States. It withered under the twin societal strains of the Great Depression and World War II.
The rise of the Counterculture in the 1960s reinvigorated interest in Druidry, and numerous other Druid organizations now exist in America, with a population of roughly 30,000.