During the war between Matilda and Stephen, Reginald, who supported Matilda, was in control of Cornwall. Subsequently forced out of Cornwall by Stephen's forces, Reginald lost the earldom to Alan of Richmond. By 1141, Stephen's forces had been beaten and Reginald was invested with the Earldom of Cornwall by his half-sister Matilda in 1141. In about 1173 he granted a charter to his free burgesses of Truro in Cornwall, and addressed his meetings at Truro to "All men both Cornish and English" suggesting a differentiation of nations. He served as High Sheriff of Devon from 1173 to 1174.