Chinese folk religion has been under attack from reformers, of several political persuasions, for more than a century, and its present condition cannot be understood without that.
Late Qing and Republican modernisers drew a line between religion, which was tolerable, and superstition, which was not, and local cult fell on the wrong side of it. Campaigns from the 1900s onward seized temple property and converted buildings into schools. The People's Republic continued in the same direction with more force, and the Cultural Revolution of 1966 to 1976 targeted temples, images, ritual texts and lineage genealogies as part of the Four Olds. Most assessments hold that the great majority of temples on the mainland were destroyed or put to other uses in those years, and specialists were persecuted.
The revival after 1978 was fast and largely unofficial. Temples were rebuilt from village funds and from remittances by relatives in Taiwan, Southeast Asia and the West, often on their original sites and from surviving memory. Because the state recognises five religions and folk religion is not among them, a very large number of these temples occupy an ambiguous position: unregistered, tolerated in practice, sometimes reclassified as Taoist, sometimes promoted as intangible cultural heritage for tourism, and sometimes demolished. Enforcement varies by province and by year.
This is the direct reason adherent figures should be distrusted. There is no membership, no conversion, and no exclusivity: the same person may make offerings at a temple, keep ancestral rites, consult a Buddhist monk and describe themselves on a form as having no religion, because in Chinese usage "having a religion" implies a formal affiliation they do not have. Estimates of Chinese folk religionists accordingly range from a few hundred million to most of the population depending on the question asked. The honest statement is that the practices are extremely widespread and that the number of people they belong to is not a well-defined quantity.