Presbyterian and Reformed churches together are usually put at somewhere between fifty and eighty million people worldwide, depending on which bodies are counted, and the geographic centre has moved decisively away from Scotland.
South Korea now holds the largest and most vigorous Presbyterian presence anywhere. Presbyterianism arrived with American missionaries in the 1880s, took root through an indigenous revival movement, and became the largest Protestant tradition in the country; it has also divided repeatedly, and there are now scores of separate Korean Presbyterian denominations, several with memberships in the millions. Korean Presbyterian churches are now themselves major senders of missionaries.
Sub-Saharan Africa holds large bodies in Ghana, Nigeria, Kenya, Malawi and Cameroon, and there are substantial Reformed churches in Indonesia and Brazil.
The Church of Scotland, the tradition's mother church, has lost the majority of its membership within two generations, has closed and merged parishes at scale, and now reports a membership well under three hundred thousand from a mid-twentieth-century peak above a million. American mainline Presbyterianism has followed the same curve.
The active disputes are those running through most of Western Protestantism, but conducted here in the tradition's own procedural idiom. The ordination of women as ministers and elders is accepted by the larger mainline bodies and refused by the conservative ones, and no reconciliation is in prospect. Ordination and marriage for people in same-sex relationships has been the immediate cause of the most recent separations. And the older argument about subscription, how much of Westminster a minister must actually hold, sits underneath both, as it has since the eighteenth century.