In search of new prospects for thermoelectric materials, using ab initio calculations and semiclassical Boltzmann theory, we have systematically investigated the electronic structure and transport properties of 18-valence electron count cobalt-based half-Heusler alloys with prime focus on CoVSn, CoNbSn, CoTaSn, CoMoIn, and CoWIn. The effect of doping on transport properties has been studied under the rigid band approximation. The maximum power factor, S2σ, for all systems is obtained on hole doping and is comparable to the existing thermoelectric material CoTiSb. The stability of all the systems is verified by phonon calculations. Based on our calculations, we suggest that CoVSn, CoNbSn, CoTaSn, CoMoIn, and CoWIn could be potential candidates for higherature thermoelectric materials.