25% of the Amish are Rh-

The Amish, formally the Old Order Amish, are a group of traditionalist Anabaptist Christian church fellowships with Swiss German and Alsatian origins. They are closely related to Mennonite churches, a separate Anabaptist denomination.

Rhone Valley residents show Basque-like frequencies of Rh Negatives

Blood group studies in two Old Order Amish isolates support previous evidence for genetic differences in the two groups. The more completely studied Amish community, that of Lancaster Co., Pa., revealed higher A and lower O phenotype frequencies than found in the Amish of Holmes Co., Ohio. In both groups, about one-fourth of individuals are Rh negative. Three blood group genes (Kell-positive, CDue and CDE) are present in low frequency in the Lancaster Amish, and pedigree studies identified individuals who may have introduced them to the Amish. Preliminary studies of an unusual antibody found in one Amish female provide evidence for a “new” red cell antigen which is present in about one-fourth of Americans.

https://experts.arizona.edu/en/publications/blood-groups-in-two-amish-demes

Amish began migrating to Pennsylvania, then-regarded favorably due to the lack of religious persecution and attractive land offers, in the early 18th century as part of a larger migration from the Palatinate and neighboring areas. Between 1717 and 1750, approximately 500 Amish migrated to North America, mainly to the region that became Berks County, Pennsylvania, but later moved, motivated by land issues and by security concerns tied to the French and Indian War. Many eventually settled in Lancaster County. A second wave of around 1,500 arrived around the mid-19th century and settled mostly in Ohio, Illinois, Iowa and southern Ontario. Most of these late immigrants eventually did not join the Old Order Amish but more liberal groups.

7 Regions with more than 20% Rh Negatives