Where is it followed today, and by roughly how many people?

About two billion people — a quarter of humanity — on every continent, and growing.

Self-described atheists number in the low hundreds of millions, concentrated in East Asia and Europe, within roughly 1.2 billion religiously unaffiliated people. Honest counting is hard: the words 'atheist' and 'non-religious' mean different things in different cultures.

There is no central count. Surveys place self-described agnostics in the hundreds of millions within the ~1.2 billion religiously unaffiliated — and agnostic elements are also held quietly by many believers and atheists.

About 2.4 billion people — roughly 31% of humanity, the largest worldview by adherents. Largest populations: the United States, Brazil, Mexico, Russia, the Philippines, and Nigeria.

About 15 million people — nearly half in Israel, most of the rest in the United States, with smaller communities worldwide.

About 500 million people — roughly 7% of humanity — mostly in China, Thailand, Japan, Myanmar, Sri Lanka, Cambodia, and Vietnam.

About 1.2 billion people — roughly 15% of humanity — the vast majority in India and Nepal, with large diaspora communities across the world.

About 25–30 million people — the great majority in Indian Punjab, with large communities in Britain, Canada, and the United States.

It is not counted in adherents but in states: most of the world's constitutions today declare some form of state neutrality toward religion, though what is practiced varies enormously from country to country.

Organized membership is small — national societies of thousands to tens of thousands — but its ideas are held far more widely among the ~1.2 billion religiously unaffiliated. There is no reliable global count.

It has no membership rolls; it is measured in regimes. Several dozen countries are constitutional democracies with liberal rights protections — indexes such as Freedom House and V-Dem track the number, which has declined for over a decade.

It is not counted by membership but by adherence to its core claim: polling finds majorities in many countries affirm equal rights for women, even where the label 'feminist' itself remains contested.

In form, it is effectively universal: the roughly 193 UN member states organize humanity as nations. The intensity of nationalist feeling varies widely and is measured by surveys, not membership.