The fastest growing demographic of the US population are the Amish. Amish families are the largest in the 50 states, and the culture retains many of its members. The growth rate was thought to be exponential, doubling every 20 years. New census data from 2010 reveals that the Amish population is actually doubling every 14 years, give the 10% growth from 2008 (227k) to 2010 (249k).
http://en.wikipedia.org/wiki/Amish
Given their new current rate of growth, here are the projections for the number of Amish living in the US in the future:
250k 2010
500k 2024
1m 2038
2m 2052
4m 2066
8m 2080
16m 2094
32m 2108
64m 2122
128m 2136
256m 2150
Future estimates of total US population are iffy, with a range somewhere between 280m (given a increasingly negative birth for developed nations) to 1 billion by 2100.
http://www.mnforsustain.org/united_s...owth_graph.htm
If we take the average growth and estimate 600m Americans in 2100, about which time 20m will be Amish, or 3% of the population. The total population will be around 800m in 2150, at which point 256m will be Amish.
If American birth rates fall like a typical developed nation, and it stands at 280m in 2100, Amish will comprise 7.5% of the total population. The startling thing is what happens between 2100 and 2150. Amish would go from 7.5% to almost matching the entire population, and the US becomes an Amish nation.
Certain regions of the country will probably go all-Amish first. Ohio has the largest population of Amish of any state in the union, so they would probably go Amish much sooner. Ohio has 11m total residents, 67,000 of which are Amish. That would reach 1m Amish residents by 2066, or 10% of the total current population. By 2100, there will be 10m Amish in Ohio. Pennsylvania, Indiana, and New York, with their large Amish communities, will likely also undergo a transformation in the 21st century to an Amish-dominated region.
The bottom line is, unless non-Amish Americans start having lots and lots of babies, in 150 years, America will be Amish.