The Iron Age in Central Europe is defined as a transformative time in local populations' lives including dietary patterns. Stable isotope analysis has become a valuable tool for investigating paleodietary and paleomobility patterns in ancient societies using samples of human and animal skeletal remains from individual burials. This is an isotopic study of collagen and apatite from Iron Age Liburian burials seventh to first century BC from Nadin‐Gradina, Croatia. Sixty human samples include 40 teeth and 20 bones. Fifteen individuals with paired tissues (teeth and bone) are used to explore differences between early and later life isotope compositions. Zooarchaeological remains from the site help approximate local dietary baselines of domesticated and hunted animal sources (n = 22 bones). Samples produced excellent collagen and uncontaminated carbonate yields to measure isotope ratios of carbon (¹³C/¹²C) and nitrogen (¹⁵N/¹⁴N). Overall, the dietary indicators are quite uniform, δ¹³C average −19.1 ± 0.6‰ and δ¹⁵N average +9.8 ± 0.6‰ for bone and almost identical values for sectioned crown and root tooth dentin. This suggests a consistent lifetime diet with strong reliance on C₃ plants such as wheat, oats, and other vegetables and that there was a moderate amount of animal protein, but unlikely including marine sources. This isotopically homogeneous dataset suggests that Iron Age hillforts and agricultural settlements in this region had relatively stable diets that were distinct compared with other nearby inland sites where millet was more prevalent. This research expands our understanding of a shift toward more localized subsistence strategies in the region and Nadin‐Gradina itself.