Angkor Borei is a protohistoric (ca. 500 BCE − 500 CE) site in southern Cambodia (Takeo Province), on the western edge of the Mekong Delta. Cambodia’s protohistoric period, concurrent with the Iron Age elsewhere in mainland Southeast Asia, is a period characterised by major socio-political transformation: early state formation, incorporation into the South China Sea network, and urbanisation. First occupied in the mid-first millennium BCE, Angkor Borei became the delta’s largest regional centre during the Funan period (c. 1st-6th century CE). This study builds on previous skeletal chemistry research, increasing the sample set by additional 15 individuals, to refine our understanding of the residential behaviour and exploitation strategies of the Angkor Borei mortuary sample. Using strontium, oxygen, carbon, and nitrogen isotope measurements from tooth enamel and bone, and incorporating bioavailable baseline strontium isotope data, we find that the majority of individuals have a childhood 87Sr/86Sr signature consistent with locally acquired food resources. For those individuals with outlier 87Sr/86Sr values, utilisation of the broader regional environment is suggested without the need to infer long-distance migration. The evidence for population stability at Angkor Borei during this dynamic period of increasing regional societal complexity indicates that the catalysts for change are manifold. Many factors are likely to have contributed to the genesis of early state society including social differentiation, cultural exchange, mercantile activity, residential mobility, and settlement growth, rather than one ‘external’ prime causative factor.