The Genetic Legacy of the 17th-Century American Colony of St. Mary’s City, Maryland

We analyzed the genomes of 48 individuals from 17th-century St. Mary’s City, Maryland’s founding English settlement, to trace their ancestry, examine the enduring legacy of this colonial American founder population, and demonstrate the efficacy of using an identical-by-descent (IBD) approach to link historical individuals to the present. In our analysis, we identified over 1.3 million genetic relatives of the St. Mary’s individuals among consenting research participants in the 23andMe Research Institute’s database. We found high rates of genetic sharing with participants from western England and Wales, suggesting a likely place of origin for many of the colonial city’s earliest inhabitants. Additionally, we observed strong genetic connections with participants from Kentucky, mirroring a recorded post-Revolutionary War migration of Maryland Catholics to that region. By further integrating genealogical information from present-day research participants who share the closest genetic connections to the St. Mary’s individuals, we propose possible identities for three sequenced historical St. Mary’s City residents, including Thomas Greene, the second governor of the colony of Maryland. This unique case study highlights the power of genetics to restore lost identities to the historical record and reconstruct ancestral relationships by tracing localized signals of biogeographical ancestry.