We describe a previously unreported left humerus of the Late Cretaceous toothed seabird, cf. Ichthyornis sp., from the basal Lincoln Limestone Member (late Cenomanian) of the Greenhorn Limestone Formation in central Kansas. This specimen represents one of the oldest bird specimens in North America, and together with previously described ichthyornithid specimens, it also provides new insights into the size distribution of the fossil taxon. Our analysis indicates that Ichthyornis body size remained relatively consistent throughout its temporal range from the Cenomanian through the Campanian. The present fossil record suggests that Ichthyornis measured up to about 0.5 m in skeletal wingspan, 0.2 m in height, and 0.3 m in skeletal length.