There is no reliable count. Census and survey figures for Wicca and paganism exist in several countries and are not broken down by tradition, so the number of eclectic solitary practitioners cannot be extracted from them, and figures offered for it are guesses. What the general figures do show is that pagan self-identification grew substantially through the 1990s and 2000s in Britain, the United States, Australia and Canada, and that the growth was overwhelmingly in unaffiliated practice rather than in covens.
The distribution of the practice has followed its distribution channels. Cunningham's generation of authors reached readers through bookshops; the 1990s brought television and film treatments that produced a visible wave of teenage practitioners; the internet brought forums, then blogs, then, from the 2010s, short-form video, which is now where a great deal of transmission happens and where its quality is least controlled.
Two consequences are worth naming. The first is that eclectic practice has drifted a long way from Wicca as Gardner left it, absorbing material from traditions with living communities who did not consent to the borrowing, and the resulting arguments about appropriation are among the sharpest in contemporary paganism. The second is that a religion without institutions has no mechanism for correcting bad information, and a great deal of what circulates (including confident claims of ancient survival, and the nine-million figure for the witch trials, which is false), has proved impossible to dislodge.