A new study says that the population of North American Amish has increased by nearly 10 percent in the past two years, causing many communities to turn westward in search of new land.

Conducted by the Young Center for Anabaptist and Pietist Studies at Elizabethtown College in Elizabethtown, Penn., the study found that Amish communities in the U.S. have dramatically increased in size over the past decade.

The Amish population in the U.S. has more than doubled in the past 10 years. The current annual increase hovers at about 5 percent, meaning the population doubles approximately every 16 years.

The largest increases were in New York (19 percent), Minnesota (9 percent) and Missouri (8 percent). The total Amish population in the U.S. is around 250,000, the study said.

Although practices can vary between groups, the Amish are typically known for their plain dress, strict discipline, and avoidance of technology. They traditionally subsist on farming and small businesses like furniture shops.

“The big story is their rapid growth,” said Donald Kraybill, professor at Elizabethtown and director of the study, in an interview.

With a rise in population, however, comes a need for fertile farmland, which can often be expensive.

In Pennsylvania’s Lancaster County, known as the unofficial Amish heartland, costs can reach $15,000 an acre. Elsewhere in the nation, however, that price can drop to $2,000 or $3,000.

This push for land has encouraged Amish communities to look as far west as Colorado and South Dakota.

But why the significant increase in population? Kraybill cited cultural and theological practices that are unique to the Amish: large families with as many as five or six children, and marriages from within the communities.

Kraybill said the “loosely coupled, sort of extended family” church structure could also play a role. While mainline Protestant churches continue to see downward trends in numbers, the Amish are bolstered by an approximate 85 percent retention rate.

Ministers are chosen from within congregations by means of a biblical process known as casting of lots. Although lacking formal theological training, the practice of calling Amish ministers seems to contribute to the high retention rate, he said.

“The point is that there's never a leadership shortage as is typical with mainline groups,” Kraybill said.