The formation of Northeastern Rus in the 10th-11th centuries is usually regarded as a process triggered by intense multicultural interaction and the influx of new settlers from the Dnieper region, Northwestern Rus, and Scandinavia to the Volga-Oka watershed. The dense rural settlement network that existed in 1000-1300, which was recently documented in central Northeastern Rus, and the reconstructed medieval landscapes unambiguously suggest that the prosperity and stability of villages was an important factor in the rise of the region. The level of mobility of the population in Northeastern Rus in the 10th-12th centuries is highly relevant to this issue. This parameter can be assessed using paleodietary data on the isotopic composition of strontium in the dental enamel and bone collagen of individuals buried at medieval cemeteries. The analysis of such samples from a large, rural agglomeration dating to the 10th-early 13th centuries, Shekshovo-9, suggests that this was a culturally diverse and wealthy population, which was part of a trade network. The migration level in this agglomeration was estimated by the results of the mass spectrometric analysis of samples from 24 humans and three animals from the Shekshovo-2 and -9 cemeteries. The reconstructions indicate a high proportion of locals as compared to similar sites in Eastern Europe. No direct relationship was found between the presence of artifacts introduced from other cultures and the isotopic profile of first-generation immigrants. The resulting pattern, indicating a high proportion of native individuals, has no parallels among the 10th-11th century sites in Eastern and Northern Europe represented by comparable data on strontium isotopes.