Monadnock Mountain, also called Mount Monadnock, is an inselberg located in the town of Lemington in the Northeast Kingdom region of the U.S. state of Vermont. The mountain overlooks the Connecticut River and the town of Colebrook, New Hampshire to the east. At its highest point, the mountain is 3,148 ft high. At the summit, an old fire tower offers excel…Monadnock Mountain, also called Mount Monadnock, is an inselberg located in the town of Lemington in the Northeast Kingdom region of the U.S. state of Vermont. The mountain overlooks the Connecticut River and the town of Colebrook, New Hampshire to the east. At its highest point, the mountain is 3,148 ft high. At the summit, an old fire tower offers excellent views of both Vermont and New Hampshire. On a clear day, the view extends as far east as Maine and as far north as Quebec.