Objectives Written sources have provided information about the rise of Merovingian power and their territorial conquests after the disintegration of the Western Roman Empire, but the extent to which altered power relations in the newly annexed territories reshaped regional and local communities is poorly understood. The early medieval cemetery of Dirmstein, located in the Upper Rhine Valley, is one of the rare sites bearing archeological evidence of simultaneous use by an indigenous community and newcomers from outside the Merovingian core area, and it offers the opportunity to investigate residential mobility at the former Roman Rhine frontier during the Merovingian period. Materials and Methods We conducted strontium, oxygen, and carbon isotope analyses on human tooth enamel recovered from 25 sixth century inhumations at the Dirmstein cemetery to establish the presence of newcomers to the Upper Rhine region. Results The low δ13C values exhibited by the Dirmstein individuals revealed ingestion of a C3 terrestrial based diet, with no detectable contribution of C4 plants, which indicates the absence of individuals from regions where a C4‐based diet was common. Human 87Sr/86Sr values well outside the local range of bioavailable strontium, in combination with low δ18O values, suggest a notable presence of newcomers from more eastern or high altitude regions. Conclusions The isotopic evidence indicates that residential mobility was important and new settlers, most likely from outside the Merovingian core area, contributed to the settlement of the northern Upper Rhine Valley during the sixth century AD.