Members of this Anabaptist Protestant sect moved from Europe in the 18th and 19th centuries and founded communities in northeastern state of Pennsylvania, Ohio and Indiana.
Today there are Amish communities in 28 US states and the Canadian province of Ontario, according to a study by the Anabaptist and Pietist Studies at Elizabethtown College in Elizabethtown, Pennsylvania.
While in 1992 the researchers put the Amish population at 125,000, that figure rose to 231,000 in 2008 -- an 86 percent increase.
During that period, Amish communities were founded in the states of Arkansas, Colorado, Maine, Mississippi and West Virginia. Meanwhile the Amish population grew 400 percent in Virginia, 200 percent in Kentucky, and 150 percent in Montana.
Report author Donald Kraybill, a professor at Elizabethtown College, said the Amish growth is due in part to having large families of five children on average.
The Amish also have a high "retention rate" among their young adult members: four out of five youths, who at the age of 18 are allowed to visit the outside world and given a choice to leave, decide to remain Amish, according to the report.