According to the United States Census Bureau, the town has a total area of , of which is land and is water, comprising 6.27% of the town. The town is bounded by the Connecticut River (which is also the state boundary with Vermont) to its west and the long ridge of Gardner Mountain to the east. Signal Mountain, a knob on Gardner Mountain, is the highest point in Monroe, measuring above sea level. It has long been a major surveying reference point for maps and plats of the area between Mount Mansfield and Mount Washington.: