'Plain People' is an umbrella term. But between groups — a chasm.
Amish
Strictest. No electricity, cars, higher education. Buggies. One-room schools. Farmers. Location: mostly Ohio, Pennsylvania, Indiana. 400,000+.
Mennonites
'Cousins' of the Amish (shared roots — Anabaptists). Wide spectrum: from Old Order (similar to Amish but with cars) to progressive (jeans, iPhones, universities). 2 million worldwide. In Africa, Asia, South America.
Hutterites
Communes (common property — everything belongs to community). Use technology (tractors, electricity). Live on large farm-colonies (50-150 people). 50,000. Mostly Montana, Dakota, Canada.
Quakers
NOT Anabaptists (different roots — England, 17th century). Pacifism, equality, silent worship. Modern Quakers are progressive (Richard Nixon was a Quaker). Not 'Plain People' in strict sense.
Key Difference
Amish: isolation from world = salvation. Mennonites: presence in world + witness. Hutterites: common property = biblical ideal. Quakers: inner light in every person.