When will the Amish population growth rate slow down?

[Agafin]

It has to at some point, right?  But looking at the data, their population growth rate doesn't appear to be slowing down so far, still hovering well above 3%, with a fertility rate above 7 children per woman. But how sustainable is this? There are 360 000 of them and at the current rate (doubling of their population in less than two decades), they will reach over 1 million people by 2050 and over 6 million by 2100. At that point, Midwestern and New England states like Ohio or Pennsylvania would be experiencing population booms the likes of which they haven't had in centuries. But this all seems impossible so when do you think their population growth will start declining? And what will be the cause?

Normally, decline in birth rates occur when countries get more developed and women get educated. But given that these people live in North America which has already undergone that transformation and yet they managed to resist it, can it still happen to them?

[It’s so Joever]

A lot of them may assimilate out of the “Amish way” probably which will cause them to both not identify so much as Amish but more importantly will reduce their birth rates. This will be most prevalent in Lancaster, less so in rural Ohio but still a trend. This will probably be enough to slow down the actual rate of self identifying Amish by the 2050s.

Another likelier possibility is that the actual church liberalizes which is hard to imagine now but not impossible. That will mean the birth rate will decline eventually like with Catholics in Quebec.

[ingemann]

As long as they have access to cheap agricultural land to establish daughter colonies on, there’s no reason to expect their growth rate to change. It’s only when they have to shift to a different and less agricultural lifestyle you can expect their population growth to decline.

[President Punxsutawney Phil]

Voted "Never" because it's always likely they have agricultural land to farm on and a place for them to do their lifestyle.

[Oryxslayer]

An insular community can adjust its surroundings and its least stringent dogmas to maintain its insulation against the outside world if it no longer can live exactly as it always did. Many orthodox Jewish sects effectively died during the holocaust,  but have been given new life in 21st century towns and neighborhoods but to their specifications. So unless the bear is poked, traditions will endure as long as somebody is committed to the identity.