The seasonal and interannual movements of the American Kestrel (Falco sparverius) are not fully understood. Although one of the most widespread and abundant raptors found in North America, information on where many populations summer and overwinter is lacking. We used stable hydrogen isotope values obtained from feathers (δ 2 Hf) of known origin to create agespecific calibration functions for juvenile and adult American Kestrels. We then used these calibration functions to determine the most likely summer origins of the American Kestrels that wintered in northern and central Illinois during 2015-16, classified these individuals as yearround residents or wintering migrants, and validated these predictions with a test dataset of known origin birds withheld from calibration function creation. The latitudinal band stretching from ~44.20°N to ~48.00°N, which runs from central Wisconsin to northern Minnesota when 2 considering areas north of the winter capture locations for the sampled individuals, contained areas that were consistently predicted as potential summer origins for those classified as migrants, suggesting the possibility of a northward shift in their wintering distribution. Our analyses also found that the ratio of residents to migrants in northern and central Illinois is between 1:1 and 3:2, suggesting that migrant individuals compose a considerable portion of the American Kestrels wintering in this region. This approach provided a robust methodology for assigning summer origins to both juveniles and adults, which previously has been unsuccessful. Application of this approach allows for the monitoring of population level changes in annual movement patterns, which is essential to tracking future range shifts caused by land-use or climate change.