America's low-technology Amish sect has doubled in size since 2000 and will hit 1 million members this century as it spreads far beyond its Pennsylvania heartland, new research shows.

Steven Nolt, an expert on the Amish, told DailyMail.com that its 378,000-strong US population was doubling every 20 years, thanks to families with lots of children who most often stick to the faith.

Amish communities have spread beyond their traditional areas of Pennsylvania, Ohio, and Indiana, with fledgling outposts as far afield as Maine, Florida, New Mexico, Texas, and Idaho, said Nolt.

The expansion underscores the tightness of a group that eschews technology to focus on family time, even as modern America grapples with cell phones and social media that may harm kids' mental health.

Still, the group remains dogged by revelations from runaways about an ultra-conservative Christian lifestyle, most recently including the adherent-turned stripper Naomi Swartzentruber, 43.

'We can anticipate 1 million Amish well before the end of the century,' Nolt, a history and Anabaptist studies professor and director of the Young Center for Anabaptist and Pietist Studies at Elizabethtown College, told DailyMail.com.

He foresaw further Amish expansion across rural parts of the Mountain West and Southeast.

'There will be more Amish living in more places, with new neighbors,' he said.

'That does pose the possibility of potential misunderstanding. But also the possibility of keeping some rural areas alive and populated in the face of otherwise predicted rural depopulation in the next 50 years.'