Schema.org has a new usage statistics dataset in collaboration with Google:

> This initiative, a collaboration between Google and the Schema.org community, aims to provide greater transparency into how different Types and Properties are being utilized by developers and publishers globally.

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> The dataset, updated monthly, offers a high-level view of term usage across millions of domains. To maintain stability and respect privacy, counts are aggregated at the domain level and presented in popularity range buckets.

Here's the announcement with more context, and here's the documentation with more practical details.