We present the design and development of the DEdicatedMONitor of EXotransits and Transients (DEMONEXT), an automated and robotic 20 inch telescope jointly funded by The Ohio State University and Vanderbilt University. The telescope is a PlaneWave CDK20 f/6.8 Corrected Dall-Kirkham Astrograph telescope on a Mathis Instruments MI-750/1000 Fork Mount located atWiner Observatory in Sonoita, AZ. DEMONEXT has a Hedrick electronic focuser, Finger Lakes Instrumentation (FLI) CFW-3-10 filter wheel, and a 2048 x 2048 pixel FLI Proline CCD3041 camera with a pixel scale of 0.90 arc-seconds per pixel and a 30.7× 30.7 arc-minute field-of-view. The telescope’s automation, controls, and scheduling are implemented in Python, including a facility to add new targets in real time for rapid follow-up of time-critical targets. DEMONEXT will be used for the confirmation and detailed investigation of newly discovered planet candidates from the Kilodegree Extremely Little Telescope (KELT) survey, exploration of the atmospheres of Hot Jupiters via transmission spectroscopy and thermal emission measurements, and monitoring of select eclipsing binary star systems as benchmarks for models of stellar evolution. DEMONEXT will enable rapid confirmation imaging of supernovae, flare stars, tidal disruption events, and other transients discovered by the All Sky Automated Survey for SuperNovae (ASAS-SN). DEMONEXT will also provide follow-up observations of single-transit planets identified by the Transiting Exoplanet Survey Satellite (TESS) mission, and to validate long-period eclipsing systems discovered by Gaia.