Polymer composites of polyolefins and dried distillers’ grains (DDG), a coproduct of corn ethanol industries, are investigated. The matrix contains polypropylene (PP), maleated PP (PPgMA), and maleated ethylene-propylene-diene monomer rubber (EPDMgMA). Utilizing DDG as a filler and/or reinforcing agent in novel bioreinforced polymer composites ultimately leads to value-addition to this material and increases its profitability to the corn ethanol sector. Several mechanical, thermomechanical and physical properties are investigated in this work. By implementing statistical methodologies and tools to optimize the composite formulation, it is observed that replacing PP partially by 10, 2.4 and 2.2 wt% of DDG, PPgMA and EPDMgMA, respectively, results in a composite formulation with mechanical and physical properties very comparable to the studied neat PP but with higher bio-based content. Also through statistical analysis, a composite formulation is identified that exhibits more than 200% improvement in impact strength compared to the studied neat PP.