We reviewed historical patterns in distribution and investigated dietary habits of a relict population of cardinal shiner (Luxilus cardinalis) in southeastern Kansas. Historical (pre-1980) collections of cardinal shiner ranged throughout portions of the upper Neosho and Verdigris basins, and contemporary collections (post-1980) documented the species in many of the same locations. Reduction in cardinal shiner range has apparently occurred in the Neosho River basin just downstream of John Redmond Reservoir. Diets of 95 individuals collected from five sites in the Cottonwood River drainage of the upper Neosho River basin during summer of 2010 included primarily aquatic invertebrates (occurred in 93.7% of individuals, constituted 29.3% of diet), followed by terrestrial invertebrates (76.8%, 9.5%) and algae and plant material (70.5%, 4.8%). Diet diversity increased as cardinal shiner size increased, so that aquatic invertebrates constituted the majority of the diet among cardinal shiner >80 mm total length. Although previous studies conducted in Oklahoma suggested cardinal shiner consumes nearly equal amounts of invertebrates and plant material, our findings suggest the relict population in Kansas consumes primarily aquatic invertebrates and occasionally terrestrial invertebrates and plant material.