Frontal polymerization (FP) is a self-propagating reaction in which the reactive zone propagates through a monomer solution at a steady velocity. Using FP, polymeric materials are cured rapidly with minimal energy input. Here, we produce high-glass-transition-temperature thermosets via frontal ring-opening metathesis polymerization (FROMP) of dicyclopentadiene (DCPD) with norbornene-based cross-linkable co-monomers that enable tuning of the cross-link density. The glass-transition temperatures of poly(DCPD) systems are systematically varied from 138 to 219 degrees C by altering the amount of cross-linking co-monomers in the resin. Front velocities exceeding 5 cm.min(-1) enable rapid, solvent-free production of thermoset materials with a 99% degree of cure and yield strength of 57 MPa. The DCPD-norbornene co-monomer resins are cured with 6 orders of magnitude less energy than a traditional oven cure and have a T-g nearly 90 degrees C higher than reported thermosets of DCPD prepared via FROMP.